Many grants require an official record be kept of day-to-day research activities. For experimental research groups, this is often accomplished with a bound paper notebook in which the experimental details, troubles, and possibly a few key results can be written (or sometimes even printed off and taped in).
Some electronic lab notebook options exist, which may be better suited to work done entirely on the computer (or maybe not!), but these are still less common. Plain text files may not satisfy the requirement of immutable entries. Furthermore, some institutions and groups with a tradition of experimental work may not take to an electronic format at all.
What methods have you tried to keep an official log of your computational research activities?