Probably the most useful thing (imo even above vet practices past the first 2 weeks) is farms. Especially if you can get lambing (but obviously that is seasonal to spring) or calving, it is very hands on and gets you prepared for all the 'realities' of the career with long hours, all weathers, physical work, difficult/stressful situations, all types of fluids, losses etc. But I would ideally to get a mix of small animal (kennels/catteries/shelters), farm and equine. Riding schools usually love an extra pair of hands and are used to teaching beginners the basics of horse care.