I think a lot of people (including graduate students) have a very poor idea of what a post-doc actually does with their days. And opinions seem to differ, as evidenced by the discussion over at youngfemalescientist as of late. So in my vast experience in a month and a half as a post-doc, I thought I'd try to discuss what I do with my post-doc days.
As a post-doc I don't have the one focused project that I had as a graduate student. Sure, there's one project that providing most of my funding, but that doesn't occupy a proportional part of my time now - nor will it over the long-run. Instead, I have something like 4 projects, all with competing timetables. Not all of these projects are particularly related to each other - they are at different scales, use different methodologies, and are at different stages (from design to publication).
As a post-doc, I don't just do my own research. I am trying to get my undergrad to finish his thesis, which is taking more and more of my time as he gets down to his final weeks, and produces frequent draft fragments. I am also helping a MS student in our group with some modeling in order to reduce her workload as she tries to meet a grant deadline. After this immediate deadline, I imagine I'll stay somewhat involved with her research as it has significant topical overlap (though not methodological overlap) with my funded project. I also contribute ideas, critiques, and/or labor to projects that S and Boss are working on, usually with short time-frames.
As a post-doc, I am expected to develop new project ideas and contribute to grant proposals. Unlike the biomedical fields, it is rare in -ology to have six digit multiple year grants which can fund an entire post-doc or PhD, so the process of grant-writing is much more ubiquitous. Especially if I want to keep my job past this year. To wit, Successful Woman called me up on Friday and asked me to contribute to a small grant proposal due in mid-month. So I spent a couple of hours learning some background information this afternoon.
As a post-doc, I am going to spend a fairly significant chunk of time looking for a permanent job or my next post-doc. It may not be part of my job description, but it is indelibly tied to the transitory nature of post-docs. I have funding for one year. That means that if I want to be using my PhD this time next year, I need to find a job. Maybe I shouldn't be doing this "on the clock," but the "clock" is just as elusive as a post-doc as it is during graduate school.
As a post-doc, I am going to devote some time to getting my dissertation chapters publishable/published. Fortunately in my case this is one of my "assigned" projects, because my advisor/boss as co-author has something at stake too. This one also goes with the previous one, as pubs become even more crucial to getting jobs, even at SLACs.
Other things I do as a post-doc: review papers for journals (and not just under my advisor's name), attend relevant seminars and meetings, stay marginally current in my field(s) by skimming table of contents and abstracts of journals, and deal with the hassles of university administration in order to get paid and get benefits.
Yep, that's what I do. No wonder I am having trouble summarizing it in one to two sentences for my CV. And I don't think my in-laws will understand it any better than they did when I was a graduate student.