Frugal

As fiction goes, it's relatively plausible - Watney's a good enough botanist to be selected for the space program, and in the bit of the novel/film he's working on potatoes, he's not doing much else, so can dedicate as much time as is necessary to get what he needs. For plot-convenience reasons, he's in a situation where he's got enough space, starter potatoes and existing food to make it all work, too. Andy Weir got those quantities by consulting experts rather than guessing, so they should be realistic.