10 and 12 are the most common, so I take ratchet and sockets to make the majority of jobs easier/quicker. other sizes I use spanners because they are less frequent and there's no point in duplication. For example an oil change needs a 17, 13 and 12 plus an allen key. it's a 12 to get the seat off. a 12 to get the tank off. For me sockets are a luxury.
true, I can't do major surgery to the bike with these tools. But I wouldn't want to do that at the road side. I'd get to a large-ish town and find a bike/car shop to use. I've found they are fine about lending the odd spanner if you buy the parts/oils from them.
It's like your clothing luggage. Do you carry a tux, just incase you're asked out to a dinner/dance?
when reducing my old over-weight toolkit I just put it down next to the bike, changed the oil, adjusted the chain, removed the wheels and replaced the brake pads. Every tool I used made it into my toolkit, the rest I left behind. That's realistically as far as my knowledge extends for now. When I learn to use a multi-meter over a test-lamp then I'd probably carry one.
Probably going to need some exotic tool I left at home when I'm away over the next few weeks. I'll feel a right fool then...