Start by taking everything out. I bet you’ll find a lot of stuff that is waaaay past its use by-date. Throw that away. Just do it.
Take all the half-empty bottles or tubes next. Roll the tubes up nicely, and you’ll find that they suddenly take up a lot less space. The bottles you’ll have to decide whether to keep or throw away. If you haven’t used them (or even seen them!) for the past six months: throw them out, you don’t need them.