Recently had the same question from my nephew. This list is comprehensive and several items are a given with the purchase of a used older vehicle, but as always it depends on your budget.
-Wiper blades - check/replace
-Washer fluid - check pump function and spray pattern (while driving) and use deicer fluid.
-Battery and charging - check/replace
-Belts - check/replace
-Tires - preferably snow tires/aggressive, check tread depth, tire pressure @ cold temp. Chains for deep snow area
(small tarp to lay on).
-Oil - 5W… synthetic.
-Transmission fluid - check for cleanliness and level. Go with synthetic for cold temps.
-P.S fluid. Check for cleanliness and level. Go with synthetic for cold temps.
-Drive train fluids - check for cleanliness and level. Go with synthetic for cold temps.
-Coolant - check level and correct mixture for lowest temps in your area.
-Undercarriage - rust prevention, check for rusty exhaust clamps or anything loose.
-Spare tire - remove and inflate/balance, grease hardware, confirm all hardware is present required to change a tire.
-Exterior - wax or provide a protective coating.
-Lights - check operation and consider brighter headlights. The stock candle lights need some improvement.
-Interior - winter mats to keep slush, snow and water off the carpet/floor.
-Check for adequate air flow and temp to defrost vent.
-Clean/lubricate door locks, handles, hinges, tail gate, steering linkage, and chassis/suspension.
-Keep fuel tank 1/2 full or more. Helps with adding weight to the vehicle too.
-Without a cap the bed is open to the elements. Hopefully you have a bed liner. Depending on terrain and snow depth in your region - add some weight over rear axle for added grip. With the added weight the truck may potentially handle differently (over steer etc.) so refrain spirited driving dry days.
-Snow brush/ice scraper.
-Go-bag - flashlight, cell phone charger, tool kit, shovel, jumper cables, first aid kit, extra clothing, blankets, gloves/hand warmers, and flares/warning triangle.
