I don't go on holiday, but when my dad does, he sometimes brings back a small trinket for me. When he went to Egypt, he brought back a small pyramid, and a glass of sand shaped like a dessert landscape.
I like to get things that are unique to the area, and that I know I won't find anywhere else. For instance, in Bruges in Belgium, I found a store that sold nothing but nutcrackers. They are exquisitely detailed and have every type of theme you could imagine. My husband and I bought one each, a little chef and a guy on skis with a pipe in his mouth and a tiny furry hat. They are some of my favourite knick knacks ever.
I buy either a book of recipes or a painting or sculpture. It depends what's available but I love art and have something from each place I visited. Also fridge magnets just to remind me of where I've been.
As I am a very practical person I usually buy things that you can use and can't get in Australia. I've picked up some good things. I love all sorts of street food but find recipe books in English hard to get though