Take whatever YOU think you might need for 3 (maybe more) days away from home, everyone has their own list of comforts and needs.
I’m a tramper and keep the same truck, so all I need for a week away for ME is in here, plus loads of other crud that I probably don’t need but might come in handy.
I suppose it depends on how big yer bag is to carry yer stuff, but minimum I can think of is:
Wash/shower kit, inc flip flops for in the shower!!
Food and hydration,
Something to sleep in or on.
Some pennies.
Some form of entertainment
Good luck, you’ll figure out what you do and don’t need after your first trip.