First, What engine/tranny do you have?
How much do you what to spend? Is the car going to be a daily driver?
How much are you worried about gas prices? where abouts do you live?

Just a few question to start. There is a tonne of thing that you can do. I am in the process fo restoring a 78 Firebird (smokey and the bandit). Last thing you will want to do is something that will make the car unroad friendly.

Some friendly street mods you can make are:

Dual exhaust (if it doesn't already have it).  
K&N air filter/cold air intake
You may be able to "tune" the chip on this by getting a chip from online -- this will allow you to change shift points, etc., for a more customized driving experience.

The best bang for your buck is always nos.there are kits for $400 at jegs for instance.everything is going to give you heavily inflated h.p.#.if you get a 125 h.p. nos system logically you should get 100 h.p.when you bolt on all those low budget gadgets that say up to 20 hp your only actually getting 5-6 or so.also theres nothing faster than disconecting a nos system when it comes to selling it or your car.

You can put nos if u want to blow up ur engine. Check out my camaro all the performance parts put together cost maybe $1500 and i am at 350 Hp running  a 13.3 in the quarter mile.

you can get a chip, cold air, rocker arms