Hi there -
My daughter was 2 1/2 in August, and she's usually 50-70th percentile in height & weight. She made it through the summer in 2T clothes. I had bought a few 3T summer things that she wore, just "floated" a little. She's just now hitting a growth spurt, but still fits comfortably in most 2T things. But you never know when & how much each child will grow.
The biggest impact on clothing has been what my daughter is *willing* to wear rather than what fits. I hear/read that this is fairly typical for this age. Buying consignment & eBay clothes for my daughter had become a fun hobby the first couple years, but suddenly at 22 months she refused to wear most things, and insisted on running around naked or in just a onesie (in December!) This was the subject of many a tantrum - getting dressed became a huge struggle until I just let go and let her wear what she wanted and/or kept her in the house until she'd bundle up.
She's become slightly more flexible again, but at least 50% of all the cute 2T things I'd bought for her in advance she hasn't worn at all. She only likes certain colors, textures, styles (most preferably purple, shiny, flowery, "girly", skirts/skorts rather than pants) but it's not always predictable. You won't know until next summer what kind of clothes your daughter likes to wear, and by that point I'm sure she'll have some opinions and let you know very strongly what she doesn't like. I've found the best thing is to take my daughter with me when I shop and let her give a little "feedback" before I buy. Although if I'm on my own and prices are great, it's worth the risk sometimes.
Someone had a good point, that anything you buy and can't use you can consign and redeem some of your money. Or share with a friend or your favorite charity.
Good luck and have fun.