There are lots of threads on this topic; to recap:
1. Start with things where fit is important; mask, fins, exposure suit.
2. Your regulator is the key element in your life support system. When you feel more comfortable trusting yourself rather than trusting the dive op du jour to see that it is maintained properly, buy one. In the mean time try as many different models and manufacturerers as possible and read the dive mag reviews.
3. BC or BP/W is next. Same comments as above apply.
4. Make a list of the less expensive stuff ( knife, lanyards, lights, dive bag, etc.) Be as specific as possible. Pass it out as birthdays and Xmas approach.
5. Tanks require VIPs every year ( $10-$20) and Hydros every five years ($30-$40). Add in the cost of an air fill and it takes 15 -20 dives a year to make owning a tank cost effective.
On the one hand:
The more accessible diving is to your home locale the more beneficial it is to own equipment. I live 10 minutes from the Pacific Ocean. I have everything mentioned above and more, some in duplicate, including 4 tanks, and I keep it packed and ready to go so if the visibility hits 15-20 feet ( 5-10 during lobster season) I can be in the water in 1/2 an hour instead of driving to the LDS, selecting and renting gear, driving to the the dive spot, driving back to the LDS, etc.
On the other hand:
If you are only doing resort diving, a full set of equipment can set you back the cost of a weeks dive vacation so what do you want to do: dive one week with your own equipment or two weeks with rented stuff?