Spares & tools - what do you carry and how?

As I'm mostly running big tyres now (meaning a spare tube doesn't fit a saddle pack and leave enough room for other stuff) I use a small pannier-style top-tube bag from Decathlon. Tube and tubeless repair kit in one side. Tyre levers, multitool, chain tool, spare link, tube patches, spoke key, gaffer tape, cable ties, tyre boot (doubles up as a handy emergency £20), Presta-Schrader adapter in the other. If I was buying again I'd probably get a frame bag that sits inside the triangle as to my eyes they look neater on a road bike and carry more stuff. I'd also get a bottle boss back as it would swallow the pump. 

Pump-wise I have a Topeak Mountain Morph mounted on a bottle boss. Possibly overkill for a road bike but if I'm out on a group ride (when we could that) it proves to be very popular as it'll easily get a skinny road tube up to 120psi. There's a road version available but it's usually more expensive than the MTB version. It almost makes getting a flat a pleasant experience with the fold out T handle and foot peg. Could just do with having a slightly longer hose.

Standard puncture repair kit (rubber cement, vulcanising patches, sand paper, tyre levers, talc cube, in a small plastic box)

small squirty bottle of graphite dust (since the talc cube in the repair kit disintegrates)

a multi-tool; all in Lidl saddle pack.

Zefal telescopic pump bracketed at the bottle holder.

Two AAAs and three Allen keys in the handlebar bag, because the Lidl saddle pack is a swine to open.

Everything has justified its presence through use, and nothing else has ever been required, which maybe should be two supplementary questions.

In my Cyckit Aeroclam (I have one on each bike) I carry;

1x spare tube

1x piece of old tyre 4" long with the beads cut off as a tyre boot

2x Cyckit tyre levers (excellent flat design, strong and reliable)

1x CO2 inflator

1x Topeak Rescue Box with some self adhesive patches and a chain link

3x various valve extenders to fit valves with/ without removable cores

1x valve core remover tool (tiny plastic, takes up no space at all)

I leave this lot on both bikes all the time to save swapping kit around

I then carry a small old neoprene phone case, which fitted my old iPhone 4, so quite small, in my jersey pocket. It was made by Cervo Rosso who have now gone bust. In that I carry (see picture);

1x Topeak V10 multi tool which has a chain breaker. It is very compact and excellent for its size.

1x Lezyne CO2 inflator head

1x CO2 cartridge

I carry a second Cervo Rosso case with my cable lock if I'm going to need it (just for convenience store stops on long rides etc) This goes in the other jersey pocket.

In my middle jersey pocket I carry a Rapha Essentials phone case which hold my phone, key, debit card and some cash, plus at the moment my neck buff which acts as a face mask on stops.

These cases are thin, about 1cm, so they don't fill my pockets, there is still room for chewy bars, energy drink sachets (for long rides), arm warmers, thin gloves if needed and a gilet/ rain jacket.

Depends on the bike and the journey. Pre-covid, quite often nothing at all beyond a wallet and mobile phone. These days it's usually an inner tube, pump and tyre levers.

For longer journeys on my e-bike I take a bit more stuff - spare chain, multi-tool, hex keys, cable ties, disposable gloves, small first aid kit.

I have a frame bag on my road bike, my other bikes have panniers.

Topeka Race Rocket pump on the bike, 2 spare tubes, self adhesive patches, 2 Pedro's levers, a minitool and a quick link in an Ortlieb Micro saddle bag.

I carry way too many tools, but here's my current selection:

Chain-breaker tool in handlebar
Spare inner tube and tyre levers attached to water cage (Topeak)
 

In a Rhinoware saddle dry-bag (https://www.amazon.co.uk/gp/product/B087NCGG78):
iPump mini-pump
Lifeline 2-in-1 tyre levers/inflator
Wolf Tooth multi-tool
Flexy 4mm bit extender (for use with the Wolf Tooth)
Dynaplug racer tubeless repair kit
Shimano Di2 tool
Co2 cartridge (rusty)
Gerber Dime multi-tool
Valve extender
Topeak 5Nm torque bit
6mm-4mm adapter
4mm-6mm adapter
Tyre Boot
Doc Blue sealant
Glueless patches
Rubber gloves

Just weighed the saddle bag contents and they're 450g

I carry the following.

Multitool

Chain breaker

bent piece of coat hanger for chain reconnecting

chain pins

cable ties

spare tube(s)

pump

That seems to cover most eventualities.

On my road bike (clinchers w/ tubes): spare tube, 3x tyre levers, cycling multi-tool (w/ chain breaker), quick link, tube patches, tyre boot, a few random zip ties. All in saddle bag that stays on bike. Mini-pump attached to bottle cage. This has been more than enough for any on-ride mechanical issues for many years - IMHO anything that can't be fixed with the above is not realistically a roadside repair for a day ride. Phone, money, snacks in jersey pockets. (Obviously long distance tourers might carry a bit more - spare spokes, spare tyres, new chain etc.)

Gravel bike (tubeless): basically the same plus a dynaplug. All (including mini-pump) in a smallish frame bag. I have been considering adding a couple of cannisters to the gravel bike - I understand they can help seat a tyre when a mini-pump struggles. (on the other hand, I've also heard that CO2 can degrade sealant, so might be a case of use CO2 to seat then deflate and re-inflate with mini-pump). Gravel bike is newish so we'll see how well this works out.

I used to do a bit more mountain biking too - the one thing I would add is a spare derailleur hanger. Much higher risk of hitting the derailleur off road than on, so I don't think it's necessary for the road bike. If the derailleur/hanger does somehow end up FUBAR then on the road it's also a viable solution to use the chain breaker + quick link to convert to single speed to get home.

I like having all the emergency kit on the bike permanently. For one thing there's nothing to forget. It's less faff, more comfortable and more secure than jersey pockets. Also keeps space in jersey pockets for other things.

I prefer to carry stuff in a saddle bag, rather than in pockets, as it's always with the bike and doesn't rely on me remembering to pick it up before setting off. On my road bike, I have the following in a small Topeak aero bag:
Spare tube
Patch kit
Alcohol swab x 2
Tyre boot
Chain link
Multi-tool (Topeak Hexus X)
Swiss Army Knife (SD Classic)
Latex gloves (1 pair)
£20 note
Antiseptic wipe x 2
Plaster x 3
Zip ties
Duct tape (wrapped around the CO2 cartridge)
CO2 cartridge
CO2 regulator
House key

Saddlebag Weight 514g

Pump on frame

I have a non-cycling multitool (a Leatherman); a spare tube; a pump (not a mini-pump, but not a full size frame pump either); and then a tool roll which contains a cycling specific multitool, a chain link, the tool to get my security skewers off, a pair of tyre levers, a (very) small Phillips head screwdriver, a chain tool, and a 5mm hex key.  That all lives either in my bag or pannier, depending on which i'm using.

Edit: Just remembered. I also carry a little pack of Park Tool stick-on patches, just in case.

I've had a few mini pumps over the years which couldn't hit 80psi by the roadside (without excessive effort and the pump overheating). Last year I bought a Silca Tattico (£55) which does it easily.  

It was pricey, but I don't expect to have to buy another and it's well on the way to paying its way through savings on cannisters already.