TBH it would have been cheaper in the long run for you to have got a premium..
To go up to the premium you will need to
Get the HDD,
Component cables if you have HD.
Headset and mike.
CAT5 Network cable
Wireless controller instead of wired.
But to just play on xbox live you need a CAT5 cable to your router, and a live subscription (although I think you still get a months free) initially) the headset/mike is optional but sometimes fun when slagging someone else off.