I've got a plastic sledge for pulling hay out to the field across the muddy gateway and poached areas. It's so much easier than trying to push a wheelbarrow through thick mud.
Sit up and kick hard. Got me out of a lot of sticky situations hacking on a nervous nellie who rears or bucks if he can't spin round and run to avoid something.
Using a caravan Aquaroll to get water out to the field when troughs are frozen solid.
Built a box around the tap, insulated the sides and use an old sleeping bag inside to keep the tap unfrozen.
Always carry baby wipes - useful for so much stuff, especially at events (wiping horses mouth/nose, wiping any marks off for showing, cleaning boots etc.).
Also sudocrem - brilliant stuff for cuts, skin things etc.