There is an option to play without item restrictions. This means that you could have three Focus Sashes, Choice Bands, Leftovers, etc. on your team.
EDIT: To change the battle format, I belive it goes like this (I don't have my game on me, but I'll try to confirm in the next few days):
battle > format > Singles/Doubles/etc. > rules > here you find the option that comes out saying Levels: 50 Item Restrictions: Off Pokémon Restrictions: Off > Match, Start!