Recently, I particpated in a swap on Ravelry, and in our packages we had to include:

• yarn (at least 100 yards)
• something representing my field of study
• something representing my swapee's field of study
• something hand-made

and I got some very cool gifts from my swap partner, whose area of specialization is pure mathematics:

She designed a knitted bag with the international symbol for hearing loss, and on the other side she knitted a fibonacci sequence!

There's also some handmade stitch markers, a book called "The Kingdom of Infinite Number" and some very soft yarn (Taos). This was a fun swap, and when I saw the knitted purse, I was pretty excited about this, since I have to admit I was a little boggled about how to represent my field! (But I did find something pretty cute at this novelty store near me).