I mark toiletries/shampoo/cosmetic bottles so that I know how much I use, so when the, say, shampoo or shower gel, gets down to just 7 days, I put it aside ready to take on the next holiday. Then I have exactly a week's worth so I won't run out, don't have excess weight, and won't waste any and don't have anything to bring back. Alongside that I've always done "packing lists" for holidays, and keep them in a file after the holiday, so I've got templates for future holidays, so never take too much, and I never miss anything, so don't have to make expensive last minute purchases for forgotten items at the airport or in the resort/hotel. Saves an absolute fortune over the years.
I have minimal wardrobe/shoes etc., and tend to re-buy things I like, to avoid buying things I'll not wear that may end up thrown out or gifted. Eg I'm on my 8th pair of identity walking shoes - I wear them daily as I walk to/from work, and each pair lasts an average of a year. When I open the box, I buy another pair to have a spare in the cupboard, and I buy them when they're on offer etc so I've never paid full price and never been caught out without my favoured pair. I do the same with other things like underwear (mostly same shop and style but just different colours) and again, always have some unworn new ones in packs ready to wear to replace existing ones. Same with everything else really. I like what I like and I'm not a slave to fashion, so happy to "look" the same year on year, if not decade after decade, with basically same/similar clothes from same shops! It works for me and I save a fortune.
In my childhood, you could get free train tickets by accumulating tokens from the backs of packets of breakfast cereals and some washing powders - I remember my mother buying several packets of them at a time and she'd put them on the shelf (for months!) with the cardboard cut out where the token was. That kind of memory sticks in your mind.
I absolutely detest waste (including paying for things you could get free or cheaper), which comes from not having a childhood and young adulthood with any spare money, so I had to make literally every pound count. A "growing up" habit like that never leaves you however much money you earn/save in later years.