Overnight necessities are as follows.
Big tent: 6120i has a nice layout for overnighters, fatfish 9416i are good too. 6 mans like a quickfish 6 are ok but kind of tricky to fit 2 people in depending on cot sizes and gear. I really like the 6120i for overnights, it is a shorter tent and insulated so keeps the tent warm and the heat low. You can arrange one cot on each side and have an open space in the middle to get in and out and move around, also allows you to have heater in the middle(we put it in middle at one end) so both people are equally warm. On the tent side of cot can drill 2 holes each(1 in each corner) and have room for flasher, jaw jackers etc in that space.
Cots: A must have, tent temperatures range from freezing at ground level to probably 20 deg at the roof. They higher up you get the warmer you will be.
Air mattress: The cold air is below you and without an air mattress you will feel it.
Bedding: Most people would probably want a decent sleeping bag, don't use anything too fancy though because will probably get wet or fish slimed at some point. I often just use an old blanket if it is warm enough but I am a walking furnace lol.
Floor mats: Lay these out to keep the ice from melting, increase traction and so you can remove boots.
Heater: You need a good heater, the bigger the better as you can always turn them down. Single sunflower or a big buddy with hose attachment are the way to go. Don't waste time or money with the small propane bottles. If you are using a large non insulated tent you might even want a double sunflower or just don't go out on the stupid cold days.
Cooler: If going for multiple days and spending time outside of a heated tent/vehicle you probably want a cooler to try and keep food and drinks from freezing. Make sure you bring it in the tent when possible.
Food heater: We often take a small bbq or camp stove and a jetboil. Warm food and drinks are a huge benefit especially if out for multiple days. Some people rig up their heaters to cook above them but we already had this other stuff which works better.
That is pretty much what you need minus the last 2 if just doing a simple overnight. Here are some pics of our setup when we did Lake Athabasca last year.
Hang clothes from the roof to keep them warm and dry.
