This is just a few more notes on some of the things rats love to do with regard to behavior.

One such thing is caching or stashing. This is most often done with food items. The rat will collect items of food, and run to deposit them somewhere else. The cycle is often repeated many times. Usually, food is hidden in a select location for that particular rat, with corners, nestboxes, and protected locations being most common. This behavior can sometimes be seen in nesting as well, with the rat dragging any soft or preferred nesting material into their sleeping areas. Female rats tend to do this more often than males. The reason why this stashing occurs is thought to be an adaptive trait for rats that would need to secure food for later use in times where food may not be as readily available.

Another item worth mentioning is digging. Rats do not burrow like some animals, but still seem to have a blast digging holes and pulling handfuls of dirt this way and that.

One of the most important things a rat does is sleep, typically doing so for upwards of 15 hours a day. Rats are considered crepuscular, and are most active and dawn and dusk hours. Rat positions can vary just as much as the rat themselves can, and depends on temperature, location, substrate, social situations, etc. Some prefer sleeping alone, some in groups, some in enclosed areas, and some out in the open. It all depends on the individual rat and environment.

A couple other notes on things I've seen and find interesting are these: the flank mark and tonic immobility. Flank marking is a way to scent mark but uses the flank rather than facial or genital secretions. The flank is rubbed against objects, and the rat typically leans sideways on a vertical structure, pushing the body sideways against that object while stepping forward. It is done in familiar environments, as urine marking is done more often in new environments as well. Tonic immobility is interesting as well, and occurs as a freezing behavior when the rat has pressure applied to certain areas like the upper back or nape. It can be seen when holding a rat with pressure on these areas, but is also the explanation for the immobility when a rat is on its back, having contact pressure on this area from the floor. The immobility tends to last longer in less dominant rats, interestingly.

http://www.spflrc.org/user/rats/Glossary.htm
http://www.spflrc.org/user/rats/norway_rat_ethogram.htm