Normal swimming kit, costume/trunks and goggles.  No need for a kit bag, we won’t use any of this in warm up.  Bring an extra towel so they can use the alternate to wrap up between races.  Also an extra set of ‘poolside clothes’ (loose fitting t-shirt and shorts normally) along with flip-flops for poolside.  If you have Horwich kit then this is the time to wear it!