I have a long laundry list of items I always bring. If the character cannot hold it then it is in a masterwork backpack that can be dropped or given to someone else to carry.
The first thing you need is 1 week of food/water unless YOU can create it. The person who makes food and water might die, and if you are somewhere where food/water is scarce then you might die if you don't have it.
So, 7 trail rations (3.5 lbs), 7 water skins (28 lbs). This is bare minimum, but again omit the water or the food if you can personally create that via a spell (Create food and water).
Next up is a rope and grappling hook. A knotted rope is also very handy since the climb DC is a 5 instead of a 10 if I recall. Grappling hook because you might need to climb something that you are below. Alternatively, you might need to hook onto something to drag it, slow it, or lower it. You are on a small floating dock and need to move it towards a different dock. Mage hand the hook over, hook it onto something important, and then just take 20 pulling the dock over.
Cold weather Clothes and Hot weather clothes. Make one of these your basic clothes that you get at the start, then buy the other. I think Cold Weather clothes are more expensive so use the free buy on that. This gives you a free +4 on cold checks, and I believe a +4 on heat checks.
Bedroll, winter blanket, and a tent. Sleeping exposed to the elements without a tent might sound ok, but when it starts raining at freezing temperatures you are going to wish you had a tent. Also, you are going to have to sleep out in the wilds eventually. Prepare for it.
Unless you have some sort of ability to light flammable material via magic (spark) then you are going to need flint and steel.
I usually bring a Shovel (digging), a hand axe (cutting wood to burn), a hammer (to hammer pitons into a wall for climbing), and a dagger so I can cut ropes or other materials.
Also, Pitons, you will want to either buy a climbing kit or buy pitons. These are the things you hammer into a cliff side so you can attache ropes to them in the event that you fall. Better to fall 10-ft than 100-ft.
An Iron Pot for cooking. You can do the whole ass-to-mouth spit roast if you want, but Iron Pots allow you to boil water BEFORE putting it in your water skins. Contaminated water can give you filth fever, and while that doesn't sound so bad it can kill the party quite easily.
Mess kits are nice. Fork, knife, spoon, cup, plate, bowel, and various other cooking items.
If you DO NOT have darkvision then you want a light source. Lamps and oil, torches, and everburning torches are all must haves.
Cheers.
Ten food pole, flask of acid, flask of alchemist's fire, smokesticks, tindertwigs, holy water...
If your GM allows it, try to have at least one cure potion as well.
Whatever class I'm playing I get the corresponding kit.
It's your classes survival kit with all the needed things like 5 days food rations, waterskin, bedroll, iron pot, traveler's outfit.