This DIY Solar Bag is an interesting project if you’ve got the time and energy (arf!). You’ll need lots of tech sounding components like capacitors, voltage regulators and the like, but the result should give you a trickle charge for small devices, as long as you’re facing the sun directly. Mmm…
Walking around in the city on a sunny day gave very good results because of the additional light coming from reflections off glass and bright stone walls. The charging went down when walking around the park with many trees and lot of grass. Going in and out of the trees shadows causes the iPod or cellphone to switch between charging and not charging (in the shadow) that might actually train the battery because each time when the charging starts or stops the display will be switched on which uses quite a bit of power.