Having a family has made me buy more 'things'! I used to buy the products that made extra products unneccessary but family go through products so fast, and don't care about the brand or quality. It only took one $30 bottle of shampoo to be used in a week by my step daughter (would have lasted me 3 months) for me to decide that the $4 bottle would have to do, and i would use a conditioning treatment to add extra shine to my own hair... It just wasn't going to be economical.
I like to buy products that will do two things, or that will be appropriate for more than one person. Like a good quality body moisturiser for the whole family that will also be used as a deep conditioning lip treatment and face wash, a hand and foot moisturiser. And cue-tips can be used as a make-up applicator (so i don't have to buy them separately). I don't buy blusher, but I can use my lippy, applied with a finger under pressed powder, when i want that look. That way it matches the lipstick i am using on the day. And a powerful, low-scent deoderant/anti persperant that my husband and I both use. I scent with perfume and he scents with aftershave.
I do keep a couple of products 'just for me', like my make up (all fits into a 20x10cm zip purse) and perfume. I buy a 25mL bottle of the real stuff (not body or toilette spray) and it lasts me 2 years, don't take up too much space, can easily pack in the make-up purse for an over-nighter and smell delightful all day.