[justaguyhere]

This is an easy problem to solve. Keep a to-do list for down times - small tasks that are not too urgent/important, but can save time in the long run.

If you absolutely can't find anything to do in your task list, then you could do one of these two - first : find a colleague who needs help and help them. Second, keep a diary (or text file) and learn something new that is specific to your job/company. In my case, I work on a mid sized webapp, I know probably 30% of the application - so I make it a point to learn something small here and there, and it adds up over a period of time. Yes, I am aware that this knowledge is useless if I leave this job, but until then it is very useful.