Childcare if you're in work, or go back to work. It doesn't cost much less when it's just before and after school either. We paid more in CM costs a month (for 3 days a week) than our mortgage! I'm now a SAHM
School trips, uniform, shoes, activities. We buy supermarket school uniform and luckily she doesn't have to have logo-ed stuff either. I sometimes buy a decent branded (Next, M&S) cardigan for school via eBay or similar as they do seem to last well. DD asks to do things which of course we don't have to do but it's nice to do something during the school holidays
DD is nearly 6yo and doesn't mind second hand clothes or toys, I'm sure as she gets older she will express a preference for new. I hope I'll encourage in her a sense of bargain hunting, but teenagers are going to want to shop in New Look with their friends.
Holidays. Okay, possibly a luxury, but it's expensive to go in the school holidays. Holidays were cheaper and easier with a pre-schooler. DD now costs to get into places, wants to go to places and again, if we stop for a snack/cake/drink, she also wants one (at usually an adult price).
Food. DD is hungry a fair bit and we encourage her to eat fruit/veg for snacks. That is one of the most expensive bits of our shopping!