If you can't make it to Nepal, Bhutan, or Tibet any time soon, you can order the same prayer flags that they sell there!
You can attach them to your backpack, or hang them anywhere that the wind blows -- when they blow in the wind, that means your prayers are being heard!
These are similar to the ones I'm holding in the photo, but with the traditional colors instead of neon ones, and they are a little bit larger than the ones you see on my backpack, they are 11.3 cm x 8.3 cm.