All that is really essential for me is a tube, pump, patch kit and a Quick-stick to remove/install tires. Patch kit glue tubes generally suck though, once opened they dry up quickly unless used up quickly. After getting two flats in one ride though I started carrying a tube or even two and repair the tube at home where I have a can of Slime brand tire cement from the auto parts store with the built in applicator brush. I still have the repair kit but only use it as a last resort.
Otherwise I carry regular 4,5 and 6mm allen wrenches and a home made boot made of duct tape. I've never needed the boot. I carry a couple quick links, never needed them either. No chain tool as with mushroom pins it's not like it's advisable to be pushing out a pin and reinserting it like with the Sedis chains of old. I've tried it at home but it never seemed to have the same link movement as it should. In an emergency though I would do it. I've broken but one chain in my life though, in 1983 or something. A Sedis. I now use SRAM and KMC , 8 and 9sp w/o ever an issue.
I did buy a Connex Link 9sp connector to try as they are tool-free and they can be reused many times over multiple chains. So if anyone has an issue with tight quick links on any chain(6-12sp) I'd suggest investing in some of those rather than carry a hefty chain pliers.
I loathe to eat anything while riding anymore so if I was really bonking I'd stop at a convenience store and get a small carton of whole milk and see if they had any very ripe bananas. Nice ripe bananas don't carry well from home at all.
Pretty much every ride though I go through what am I taking and ask if it's really needed. Pump, tube, patch kit and Quick-Stick, yes. My wallet is a tiny Chums and I carry my phone for an emergency ride, like a crank arm cracking mid ride which happened once. Even then, I've ridden countless times w/o anything extra and nothing happened but normaility :)
Oh yeah, the Topeak Morph pumps are the only I've used in the last 25 years. A Road, Mountain and I just got a Mini. I was so happy when I got these as frame pumps were just so wrong ergonomically for me. Having the mini floor pump is the best idea ever for a portable pump. Since riding Schwalbe 50mm Big Ben and 35mm Marathon Racers @ relatively low pressures of 30-45 psi however, I haven't needed to use them.
Right now I carry the tool stuff in either a Revelate Shrew seat bag or a small Timbuk seat bag in a bottle cage if my bag is otherwise full.
For years I rode with a Filson cloth diy tool wrap and a toe strap attached to a bottle cage. I think it was Filson, maybe something else. That was over 20 years ago. Riv sold the cut cloth squares and the user filled them with whatever and wrapped like a closed burrito. I still have both of them. Very durable, rain doesn't penetrate when folded correctly.
I think less abut carrying anything extra on my Bomba than my custom 531 Franklin road bike as the Bomba is just a tank any way it's fitted.