You have a 1911. Does it work with ball ammo? Yes?
Good, you now have the "right" gun for the game.
Do you have a a sturdy pants belt?
Good, you now have the belt for the game.
Do you have any sort of strong side holster the covers the trigger guard of the 1911? if yes then..
Good, you now have the right holster for the game.
You do not need magazine carriers as you can use a pocket but you do need at least two spare magazines.(see below)
The most important item you need is to have and have read the rule book.
Highlight the items, if any, you don't understand and ask questions at the match.(You can download the rule book from the IDPA web site-
www.IDPA.com)
It's a safe bet, the regular shooters will lend you mags for the match and maybe other stuff.
Bring a good attitude and safe gun handling habits and you're set to go.