Been there done that and feel your pain. It is really hard when that happens. Have worked agency in San Antonio, Austin, and DFW and those cancelled shifts really mess you up.
I list the agency as my employer and the city where they are located. I try to tailor things to the job I am looking for. If I am looking for a sort of run of the mill nursing job I will put something like: Worked as supplemental staff for area hospitals on Medical, Surgical, Telemetry, Oncology, and Critical Care Units.
If I need to give more detail, then I play up the fact that I am flexible and can adapt to working different assignments on different units on a daily basis. I emphasize that I have the ability to walk on any given unit and become a team player without difficulty. If there are certain procedures/assignments that are special then I will play those up as well - especially if the hospital staff nurses were unwilling to care for certain pts and I was able to do it. I had an agency job where I worked ICU but they needed a nurse that was an ICU nurse that was willing to take care of PIH pts in the L&D. The L&D nurses knew about pregnancy but had a difficult time caring for the critically ill moms when they had central lines, art lines, etc. So they taught me about OB and I was able to play up the fact that I cared for such complex pts as an agency nurse because the hospital didn't have nurses with my diverse skills at that time.
As an agency nurse you have to fly by the seat of your pants. You must be able to work with little to no guidance, direction, or support by other people. So put that down. Not everyone knows that agency nurses are always getting dumped on and have to work in bad conditions (floor short 5 nurses and they only got you that shift) and they don't realize that the regular staff often give the agency nurses the most hard pts but don't help the nurses out. So toot your own horn and let employers
know that you know a about a lot of different diagnoses and how to care for those pts and that you can switch gears efficiently to care for complex pts without any help.
Hope that helps! Let me know if I can help.