If we go on holiday where we know we can do laundry (like visiting family overseas), we spend a little bit less before going there because we can pack lighter. But yes, the kids usually need new things. DH usually wants a few new items of clothing or shoes, to feel nice in an unfamiliar place. DSD is the same. I'm a bit more casual, but sometimes I've gained weight and don't fit into my shorts anymore (😭). Sometimes I've destroyed my sandals over a previous summer.
Places without washing facilities, like a week abroad in a hotel, we'd spend way more before going. Because we'd want 1-2 changes of clothes per day (my kids are too rowdy to do capsule wardrobes), plus a rotation of two swimmers (one to wear and one to hang dry). Decent sunblock, that we can all agree to actually use, is surprisingly expensive once you get enough for a family of five.
Camping somewhere, even with laundry facilities, still has a cost because someone's outgrown their waterproofs or hiking boots. And even the Mountain Warehouse clearance bargains add up.
Tent camping surprisingly expensive, I've found: booking the pitch was cheap, but then we wanted gear to be reasonably comfortable (got down to 3C overnight in July in Scotland the last time we went... I'm not ever going again without onesies, slipper socks and Heattech layers for all... and maybe one of those underfloor heating tent mats).
The waterproof gear and hiking kit we bought for one holiday was reused repeatedly over our autumn and winter hikes, and we bought on the big side so it would last. The summer stuff we buy for warm weather holidays gets handed down to younger siblings or worn again during the seven days of summer our part of Scotland gets. Hats and sunglasses are handy on sunny days even when it isn't as warm. The new swimmers are worn at the local pool and to the beach here.
The sunscreen is probably the only purchase where I could say we've overspent, because I tend to go bananas when buying it. Oops.