With my first, I bought a ton of maternity clothes. Since I work everyday, I needed a basic wardrobe. Plus, my mom tends to spoil the hell out of me every chance she can get...a little less so now that my son is around
I just picked up a couple things, like a coat that I will need this winter, and couple pairs of pants off eBay. Otherwise, I also would peruse the consignment shops when I had time. That and I intend to borrow from my cousin who just had a baby last October. She has a lot of summery stuff, that I'll need next year.
With my first pg, I didn't wear maternity stuff until I was about 5 months along. I fit into most my shirts up until then. I just bought bigger pants, seeing as I'd need them (and did) for transition wear after the pg. So I started a 4, and was wearing size 8's up until 5 months...and wore the 8's for a couple months afterwards.