Maxpedition Falcon II Pygmy
When someone says daypack, one of the first backpacks I think about is the Maxpedition Falcon II Pygmy. Its lightweight, has plenty of room for year, and has 2 places for a 32 ounce water bottle.
Inside of the pack I carry:
First Aid kit
And a some other stuff.
In warm/hot weather camping there is no need in bringing a sleeping bag rated at 40 degrees. Instead of a sleeping bag, a US military poncho liner is used. This provides protection from the chilly night air.
Instead of a tent, a hammock is used. At the very most the rain poncho can be used as a shelter if any rain starts to fall. If a tent is brought, then bring a light weight one man tent instead of a 2, 3 or 4 man tent.