Cubby, here's what I use - I think I've got everything on it, though I do usually print it out and scribble on it / tick off as I go along - (we use this for Ireland, so similar weather to Wales!)
BED Travel cot / Sheets x 2 / Grobags x 2 / Cellular blanket/ Under-sheet duvet / Bed toys / Soothers / Gripe water / Long & short-sleeved sleepsuits / Baby listener
BATH Plastic bath? / Toys / Shampoo / Sponge / Towels Toothbrush & paste / Cotton wool & buds / nail clippers
CLOTHES Swimming togs / Shoes & sandals / Socks / Shorts / Trousers / t-shirts / long sleeved tops / rain jacket / hats x 2 / vests / cardigan / warm jacket
FEEDING Portable high chair / Plastic bib / Avent cups / Bottles / Bottle brush & liquid
FOOD Beans / spaghetti hoops / Fruit puree / Orange squash / Bagels Fruit / Marmite / Raisins / Biscuits / ICE BAG of frozen food
TOYS Stacking box selection / Toys for car journey / Trike? / Buggy
OTHER Calpol / Nurofen / cough med / antihistamine etc / Vanish powder / Sun cream / NAPPIES, wipes, Sudocrem
Cleaning products ? sponge, jcloths, baby wipes, kitchen cleaner
Changing mat / towels
Phones & charger
CDs for car
Passports
Wallet / purse
Tickets / check-in details