What Can I Do Until The Vet Gets Here If My Horse Is In Colic?

Harka is very much right. Do not whatsoever, let your horse roll or even lie down. He needs to keep moving. Walk him circles both directions, a few times each way and do not stop.
If it's sand colic, apparently beer helps and horses like beer so half a bottle at a time will go down easily.

I am no expert on horses - but I do remember that it is dangerous for them to roll as it increases the risk of them twisting their gut - so try to prevent him/her from rolling.

Just keep  your horse walking.

You r right guys if your horse rolls he may twist his bowel! Try as hard as u can to keep calm (which is something I have never been able to achieve), and walk the horse around short long distances in straight lines. If u walk the horse in small circles it will be too tempting for the horse to lie down! Unfortunately no matter how hard u try, if your horse is tempted to lie down and thrash about there is no way you are going to stop them which is so scary as the twisting can occur. I haven't tried beer but I know many top horse people that have! The difference with those people and myself is that they are experts! Colic is generally thought of as an obstruction of the bowel but any type of gut pain is known as colic. So if you use beer to break up an obstruction, and the horse actually has spasmotic? (can't spell sorry) colic from a parasite, you may risk doing more harm! I will be honest though, if my vet was away and my horse was close to dying I think I would risk it as I have no idea how to give a horse a drench! My heart goes out to you, my 23 year old horse keeps getting colic and my greatest fear is that he will get it while the only vet we have in town is away!!! I love him so much and it's just too cruel a way for the horse to die! So give the horse half a bottle to start with, walk it, then after half hour give the other half!