Loaner Gear is SCA slang for weapons and armour which are communally owned by a group for the purpose of lending them to fighters who lack their own equipment. Loaner gear usually consists of "hand-me-downs" from fighters who have replaced temporary or aging armour with better quality equipment, and as such is generally ill-fitting, in poor condition and smells bad. On the other hand, many a fledgling fighter has been very grateful to his barony's loaner gear, as it meant he could learn to fight without having to lay out a lot of money for his own armour.
The "loaner jockstrap" should be avoided at all costs, however, and is generally only included in a stash of loaner gear as a joke.
The re-enactment equivalent of loaner gear is sometimes known as club kit. The amount will vary a great deal from a few items of hard to acquire gear to complete outfits.
The club kit of re-enactment groups is generally gear that has neared the end of it's useful life, the previous owner has upgraded or involves an interpretation of history that has since been found to be inaccurate. If the inaccuracy is not too great it will loaned to new members, but if it is too great a mistake, the item will instead be retired.
In some groups the entire club will be kitted out from a central store.