Starting off with a RTR buggy is good to help keep cost down, but over time as you get use to driving and get better you will maybe want to start upgrading thing's. here a few thing i would look at getting with a new car, and gear you may want to have with you.
Ofna 650cc fuel bottle
Hot shot glow igniter
spare plugs
plug wrench
good tool set
reciever pack, dont use double A's
Byron's 30% fuel
Something to keep your gear and tool's in order, Pit bag or even a tackle box from wall mart.
find out what tires are working on your track from the fast guy's and grab a set of them
grab some front and rear arm's front and rear hubs
locktite.
there is alot more u can aquire, but these are just some of the good things to have.