Bring skis, boots, and poles on every ski trip.
Bring warm clothing, starting with a layer of fleece underwear that traps air, topped by ski pants, fleece jacket, and parka.
Bring gloves, hat, and goggles.
Don't forget a helmet; they are warm, lightweight, and cool to wear.
Prepare for the worst possible weather conditions, rather than the weather outside your home, miles away from the slopes, and likely at much lower elevation.
Many skiers find that small chemical toe warmers and glove warmers make time in the cold more bearable. These are sold widely as ski shops and convenience stores near ski resorts. They are good for several hours.
If you have a season pass, don't leave that at home.
Bring money as well.
Some skiers keep much of their gear together in a boot bag, and take time to dry out boots, gloves, hat, etc. and repack it after each trip so that they are ready to go the next time.
If it's a day trip, bring water and snacks for the trip, and dry clothes for the ride home.
If you are going to spend the night, don't forget toothbrush and PJs.
Question: What to take skiing?