Wear mostly whatever you have - There's no mystery in this advice. You're going to dress for standard outdoor aerobic exercise. That means layers work best to regulate your temperature to the level of exercise you're doing. Readily available choices are running pants and/or cycling tights (un-padded) with a layer or two of synthetic fabric long underwear, some synthetic fabric long underwear top(s) under a long sleeve running or cycling jersey, and a lightweight windbreaker or parka over this that you can either take off easily or zipper open. You might already have these things and won't have to buy much.

On your hands you'll need some light to medium weight gloves with leather palms and fingers for gripping the ski poles. Winter cycling gloves with minimal padding are an option as are even winter work gloves. Gloves without durable palms and fingers will wear out quickly and they can't be too bulky or you can't grip the poles. You'll probably want to cover your head with something and, in colder or windy weather, a neck scarf or even a lightweight balaclava comes in handy.

The point is, you can wear a lot of what you already have and you're not going to get cold when you're actively exercising - you'll probably be too warm. Also, as most know, cotton fabric, while comfortable when not exercising, will hold perspiration and is not a good choice. Fleece tends to be too warm under a windbreaker and too cold in windy conditions without one.

For your feet some lightweight hiking socks work well - avoid cotton socks. Wear what fits well with your boots. If you feet tend to get cold, you can add Gortex socks or, what's really nice, these little pre-packaged activated non-woven pads sold in many hardware stores that stay warm for hours through a safe chemical reaction.

For storage, hydration and nourishment and other stuff - You got it. You're probably going to want to wear a waist or fanny pack. These are readily available with one or two waterbottle holders and a small storage compartment. You will likely want to store your windbreaker, wax kit, some snacks, a map, and anything else you find useful to have. These other things might be some first aid stuff, a whistle/compass, some duct tape (for ski/pole repair), or some extra gloves - but do try to pack right for the activity planned.

It can never be too cold to ski - If you take a trip to Lake Placid, Ottawa or Quebec, there will be times when the day-time temperatures are near or even well below zero. These are usually bright sunny days and it doesn't stop the natives from a nice ski trip. It shouldn't stop you either. Here you have to dress warmer and may want to add an extra layer (even fleece under a windbreaker) and use warmer gloves. Face and ear protection against frostbite is a must.