Tune up tips, please?

Hey everyone. I just need to know what are the routine things done in a tune up. My '99 GA SE has 85,600 miles on it and has been using more and more gas in the past few months. I had considered trading it in, but i really don't want to lose my ass, which is exactly what will happen, so I guess I'll just keep it til the wheels rot off of it!
Anyway, just a brief list of my issues and maybe you guys can give me some advice on how to cure my woes and some tips on exactly what should be replaced or whatever with a tune up.

Trunk leaks -- abs/brake lite is on now for 2 years since battery failure, will be taking it to Pontiac Dealer for proper diagnosis on brake system --I think that I need front shocks/struts which ever applies. I am currently on my 3rd set of front brakes since I purchased it in 2001, so obviously I have some major brake issues. I have more problems than that, but too drained to list....

Trunk leak....Probably the seal that goes around the trunk.
Abs...not sure
Brakes....don't go stock. Get a nice set of aftermarket rotors and pads. They'll last a lot longer.

My trunk has been leaking latly too last night i managed to see it was the seal around the trunk. I managed to reshape with a heat gun. I recommend that u not try that.