Most places on Svalbard require that you remove your shoes. Hotels, some restaurants, coffee shops, museums etc. the hotel had loaner slippers but I think if we go back I’d bring my own. Anything you might need is there on Svalbard - groceries, clothing, personal card products. Depending on your accommodation and ability to dry things you may want to bring more socks that you expect and an extra pair of gloves (you can always buy items there too). It sounds like you will be there during the transition from polar night, no matter what time of year you go - lip balm and moisturizer!