Costumes range from a simple Santa hat to a full suit with jacket, pants, belt, boot covers, gloves and beard. Budget sets work for one party; deluxe suits in velvet or plush fabric look much better in photos and hold up for years of school events and family visits.
The beard makes or breaks the look. Cheap beards look flat and itchy; better beards are fuller, curled and attach with comfortable elastic. Check whether the beard and wig are included or sold separately.
Sizing tends to run large so the suit fits over padding. Check the chest and waist measurements, and consider a belly pad if you want the classic shape. Boot covers fit over your own shoes, while full boots cost more. Try the costume on before the event day.
For a whole group, Santa hats and elf hats are an easy, affordable way to dress up. For party wear, see ugly Christmas sweaters.