My kids hate it when the cereal gets soggy. So I've given up trying to have them put the cereal in the bowl. I give them cereal and then a glass of milk and a spoon. My kids are 7 & nearly 5. I figure as long as they eat it (cereal with a spoon, not fingers and the glass of milk) what does it matter if it's together or not. Not worth it, there are worse things they could do.
LOL on the sandals with socks. I hate that too. My kids love being barefoot, even in winter. They would never dream of putting socks on with sandals.
ETA: Getting dressed even if we're staying home all day. I don't like everyone being in the pjs all day. Even if all we're changing into is sweats/yoga pants and t-shirts. We must get dressed!
As for a fight not worth fighting I think it would have to be clothes. The only thing I enforce is weather appropriate clothing, other than that they get to pick out what they want to wear even if I think it totally clashes.