had had mentioned this before, but utilizing the different kits that you get or choose would be fun. Such as the herbalist kit to make healing potions, or the smithing kit to make/upgrade weapons and armor. The alchemist kit to make alchemist fire, resistance potions, etc. All these would take time to do, however, and they are only done if a character is staying at camp (not traveling with you), or if they are in your group, then can only be worked on during your long rests. This will also give those non-active characters something to do while they wait for you to come back. To avoid this from being abused (just spend everyday at camp), this is definitely where the rations come in. So you need to go buy/collect some before you can long rest again.
The wizard ability to learn new spells should also only happen during a shot rest. In PnP, the wizard needs to take time doing nothing else, other than copying/learning the spell from the scroll.
Have training at camp. Your inactive characters can spar, sling spells for practice and do other things related to their character, and as such they gain a little bit of experience. (This would remove the all characters whether they are in your party or not leveling at the same time when in essence they didn't do a damn thin except sleep all day at camp).
All these idea can be implemented when you go to camp, but don't have to be micromanaged which would be important.