Cheap down bags and jackets to be found on google shopper and in sales coming up. Try Argos overstock on ebay or search ebay for others for cheap down bags/jackets. Try uniqlo web/stores sales in a week or so for down jackets who are already doing cheap down jackets in store form £30 to £40. Cheap ultra light rain jackets, doubling in winter as down jacket protector, which pack tiny from good brands in Sporting Direct web/stores for £10. Always buy one size larger in all clothing. Compress bulky items down and tie with strap or just cord like gift wrapping. Unstuff at home and loft for storage. Buy vacuum compression bags from 99p/poundshop to stuff down your tent/tarps/clothes/etc which are best folded not rolled to save volume, unpack all for storage even from original product storage at home as with all gear to prolong life. 99p store sells straps/buckles in baby section too or cannibalize dead packs/luggage. Attach mat on the outside of pack. Bladders instead of bottles. Cheap folding solar shower or foldling 10 litre Gelert water-carrier for water tank for £5 to £10.
Dehydrate meat and veggies, bought or cheaply made with a dehydrating machine or a very low oven (airing regularly) or under a unused sunny window in summer (takes days). Straight pasta, flat type bread sheets, rice, mash potato & other powders, spices not sauces, long quality salami to be used for meat in cooking over many days, dried fruits, drink powders, etc. Instant oat powder to save on fuel. Also cheap thinsulate socks and caps at poundshops/Primark doubling as cozy for slow cooking to save more fuel or just to keep warm. Store food in pots. Cheap Orikaso dinner set or Seatosummit X plate/bowl/mug. Flat grill (£5 Gelert toaster which easily dismantles into two grills) and folding pruning saw from DIY stores for stove and/or tuna can and meths. Go where there's water nearby. That's my current gig. Then for even a winter weekend a 25-litre sack and side pocketed trousers will do in many cases with a little planning. My motto: "If in doubt, leave it behind".