Ask the trainer--some might want you to leave something, others might prefer to use their own. My boyfriend is a trainer. He does a lot of colt starting as well as deals with problem horses, etc. All he requires (and wants) is the horse (duh), the money, and a Coggins. If the horse has supplements or uses blankets, then he'll take that too. He sends home any tack, halter/lead rope, etc. that the owner uses--he prefers to use his own. One, he's going to start it his way, and he has the correct equipment for that (so no thank you he does not need your ill fitting tom thumb masterpiece). Two, he's more comfortable using his own saddle, etc. Three, that way no one has to worry about anything getting lost or damaged and then having to figure out who is responsible. Some trainers are like him and want the money up front (because not everyone is honest and some will mysteriously disappear with the money if they are allowed to wait, plus the money goes to help pay for the horse's upkeep); others will bill you later or require it at pickup. Make sure you ask and don't assume, because if it's required up front and you don't have it, oh well for you! Some trainers may also require proof of vaccinations, health certificate, etc., so you may want to ask in case you need something extra. Many will take your halter/lead rope just to use on your horse in the barn, even if they don't use it for training purposes, so be prepared to leave that with him. If your horse has any special equipment that he has to have (supplements, meds, blankets, protective gear, etc.) then leave those as well--better for him to use his own stuff that fits if it's something like that.