Some sort of smartphone or a camera. I am very humble. I do not believe that those things will make me much happier, but they might be handy in some situations. Definitely not worth buying with volunteers "salary".
Do you use a mobile phone at all? I actually have a friend that has an iPhone 4 but doesn't have cellular service for it. He only uses it as a camera and small wireless computer. It's actually the "phone" aspect of it that he finds intrusive to his life.
I have never bought a phone and felt much better when I had none. Probably because I do not use "phone" feature and probably because of RMS intrusive to my life. Then there is always somebody who asks why I do not have one and quickly finds in treasure drawer some outdated phone that still has the life in it. Currently it is some discontinued Sony Ericsson, with cracked screen, some unnecessary buttons are not working, but it has some o.k. camera for technical stuff and measurements I need and the most active feature is e-mail. With only few euros I get 150 mb for free, with which I can survive for at least two months of active emailing. Why I like emails: * everybody has an email; * if you lose your pre-pay, you don't have to buy new string of characters to contact you; * nowadays everybody receives emails in their phones; * I can use more than 160 symbols and with all the necessary diacritics - āēšžčŗģūņīķļō usually take up 30-50 symbols at once, which makes sms very expensive, not talking about cyrilic..; What would I do with smartphone then? More tools - wolframalpha, GPS could be handy (since handheld is too large), TED talks, linphone, RSS, QR codes are more widely used everywhere. That would significantly reduce time I waste on a desktop computer usually doing unnecessary stuff in parallel to "checking out news".