Cost: 10sp
The most common kit by far, almost every adventurer will have one of these. You will start with one of these for free, and it's not hard to replenish. It includes:
The rations are consumable; they cost 2sp per week to replace. But unless something catastrophic happens, you are unlikely to lose any of the rest of this kit.
If you are, somehow, without an adventurer's kit, then you must spend two of your three hours during each Long Rest performing survival activities—building a lean-to, gathering heather for bedding, or possibly starting a fire using friction.