Inside, it reads:
It's your birthday. Well, not actually your birthday as you weren't technically born. But it's a good day to celebrate it.
Or something like it.
Later on, the Doctor is informed this is probably rude. So, he goes out and purchases a few birthday gifts.
First, the Doctor purchases something he knows Donna will like. Chocolate truffles. Very expensive. Two might be missing out of the box.
And, something he knows he himself would like. It may be already opened.
And, on the off chance that his human self doesn't like these, there are a variety of gift cards and a note promising to not complain or bother him while he shops.
HAPPY ONE YEAR ANNIVERSARY, HANDYSPAREHAND!