These are two items that I would purchase first. They both help prevent injuries that may occur often without the protection.
Mouth Piece –
In addition, you might look into getting a long sleeve rash guard to help prevent mat burn and various forms of fungal skin infection (ringworm). There are loose fit and tight fitting versions. Less expensive brands can be found at local department stores. I bought my rash guard from Piranha Gear.
Any kind of loose shorts will work. Companies sell specially tailored fight short, but board-shorts from your local Walmart or Target have always worked for me.