When open and manned, the huts are generally run by full-time employees, but some are staffed on a voluntary basis by members of alpine clubs. The manager of the hut, termed a guardian or warden in Europe, will usually also sell refreshments and meals, both to those visiting only for the day and to those staying overnight. The offering is surprisingly wide, given that most supplies, often including fresh water, must be flown in by helicopter, and may include glucose-based snacks (such as candy bars) on which climbers and walkers wish to stock up, cakes and pastries made at the hut, a variety of hot and cold drinks (including beer and wine), and high carbohydrate dinners in the evenings. Not all huts offer a catered service, though, and visitors may need to provide for themselves. Some huts offer facilities for both, enabling visitors wishing to keep costs down to bring their own food and cooking equipment and to cater using the facilities provided. Booking for overnight stays at huts is deemed obligatory, and in many cases is essential as some popular huts, even with more than 100 bed spaces, may be full during good weather and at weekends. Once made, the cancellation of a reservation is advised as a matter of courtesy – and, indeed, potentially of safety, as many huts keep a record of where climbers and walkers state they plan to walk to next. Most huts may be contacted by telephone and most take credit cards as a means of payment.