You have gone through our 6 day acclimatization program in preparation for climbing high on Mount Elbrus. Now you have to leave your duffel bag at the hotel and carry all items up on the mountain. You will need clothing and equipment that will need to last 3 maybe 4 days.
You can leave items in your room while acclimatizing and going for the summit and because you are going up in the Gondola can will be able to bring some additional items.
Here is what we would bring with us higher on Mount Elbrus
First of all, you need to make sure you have the right back pack. I use the Deuter ACT lite 50+10 back pack. This back pack as the best back support I have experienced in a back pack. You do need to have a 50+liter back pack. You need to bring your sleeping bag and small Thermarest pillow. Some rooms do have pillows.
Mountaineering Equipment you need to bring
You need proper mountaineering boots, crampons, ice axe, Harness, 2 slings, 2 screw gate carabinars one for use on the fixed lines, the other for when you are roped together with team members. You should also bring a climbing helmet.
What clothing should you bring
For your upper body: I think having 2 long sleeve merino tops either 200 or 260 weight. Down vest, Fleece layer, water proof layer and Expedition down jacket.
For your lower body: 260 merino wool layer, trekking pants, water proof layer. You also need a lightweight liner sock. Mid weight trekking sock. Thick summit socks.
For your head: You can use a balaclava if you like. I personally prefer a warm beanie hat along with a buff that has a lower layer of fleece. Some people call them polar buffs. You need a pair of ski googles and pair in category 4 sunglasses.
Other items to consider
You should think about bringing a power bank for charging your phone. You can bring your 2 liter camel Bak along with a 1 liter nalgene and thermos flask. Note: You would not bring the camel bak on the summit night. You should bring trekking poles with snow baskets. Toiletries and personal medication and snacks.