I'm almost decided on a cook kit but the cup I'm thinking of taking is the Olicamp space saver that fits under a Nalgene bottle. I'm not doing it to mate with a Nalgene bottle but because it's a good fit for a fuel canister.

The thing is 500ml (one half liter). I see that most commercial cups for solo backpacking are 650ml.

Can anyone think of a situation where I'll regret not having something bigger?

Not sure if it makes a difference but I'm also planning on cutting the top off of a coffee can, maybe a full inch. I think I can use that as a lid and also flip it over and make pancakes (large ones, one at a time.)