There really needs to be an article on how to pack your horse to go off to the trainers.  There needs to be opinions from different trainers on what they would want from owners.  Do they need to send the horse with their own tack, boots, saddle pads, blankets etc.  How do they want to tackle supplements, send bulk with the horse, buy by the bucket and charge owner, or go thru SmartPak. etc etc etc

In my experience, that really varies depending on the trainer!  Some want only your horse and whatever halter/sheet/blanket.  Others want you to purchase your horse's clothes in their stable colors and send supplements only in SmartPacks.  I've never had a trainer ask me to send my horse's tack.  They typically have everything they need to train with as far as equipment goes.