I do until I sit back and look at all the stuff he already has.

The amount of stuff my five-pound dog owns is ridiculous. A few months ago, we loaded up a box of brand new, completely unused things that we had never been touched - harnesses, clothes, food, flea preventatives, etc. - and took them to our local humane society. That was an eye-opener - since then, I've tried not to overdo it. He already owns everything in the world he could possibly need or want.
Of course, he is so spoiled that he thinks every single bag I bring into the house has something in it for him. And he is usually right.