The thing I miss most when away is my scanner.
I've been working on my book but it turns out I need bigger scans of a lot of things. (I found the same during my last project, so I scan everything at higher res now but my aspirations have also grown.)
There are few things I can spend whole days on without getting bored, but rearranging photos and text is one. When I was little I spent hours and hours designing pages full of clip art. Making word document invitations for my birthday parties was probably more fun than the parties themselves.
There are also few things that work so well to take me out of myself. Thinking hard about a moment in my past has the power to override the present. Having a project, something unrelated to work or school, envelops me.