The only Downtown restaurant you need to know is Hash House a Go Go. Period.
Also, visit the Neon Museum nearby. Kicks ass.
Fremont St is best at night when the bands play and the light show is in full effect.
The zip line is fun.
Avoid the buffets.
Take the Deuce (bus that goes back and forth to the Strip) instead of a cab.
Stay at the Golden Nugget and take the water slide thru the shark tank.