>>534744161
I like to use my high level spell slots on summoning myrmidons or planar allies on the people who will be joining the party and leaving camp, and then on the people who will be staying at home today I'll use their spell slots on aid and hero's feast. The summons actually benefit from the buff spells.

But be careful with this kind of stuff, because you can accidentally make the game too easy. When your water myrmidons have like 200 hp, there are some aspects of the game that will become imbalanced. Camp casting is a little boost to help you get through tough parts of the game, but you need to use your discretion to make sure you're not getting comfortable and used to it, or reliant on it.