When I'm visiting archives or libraries, I need to make sure that I have all the information I need with me. There's nothing more infuriating than travelling somewhere to do some research, only to discover that you have left that vital piece of paper at home!
One way I make sure that disaster doesn't strike is to write my research plans before I start in Microsoft OneNote. If you use the Microsoft Office suite of programs, you may already have this on your computer - it's that purple square with the 'N' in the middle :) There are other similar programmes such as Evernote, but this is the one I use. I can put in here the information I have and plan out which documents I need to look at when I'm at the archives.
The thing about OneNote that I love is the free app that works on my iPad - if I sync all my OneNote files via my Windows Live ID (a Hotmail account also works) they automatically download to my iPad. Likewise when I get home, any changes I've made while I've been out are synced back to my computer. So all I have to do is to type into OneNote what I find, and it's right there - no transcribing back or transferring files, it's all done automatically.
The only thing I would say is that not all archives and libraries have wi-fi internet access, so remember to sync your files before you leave home.