Boy, that's kinds like asking "how high's up?" and it really depends on the current condition of your car and it's wallet! Since you asked, my choices would be 1- add disc brakes, 2- re-do the electrical. 3- go to a bigger wheel, 4- upgrade suspension, 5-A/C if you really think it necessary, 6- carpet and 7- transmission. Several of these things can be done relatively inexpensively, but most will cost quite a few quid, especially if you're not up for doing them yourself. At the end of the day, it's your car and your call. Good luck.