An important note: Never work off the clock!
1) If you make a mistake, you will be on your own. You will be liable and Kaiser (for Kaiser employees) or CVS (for CVS employees) will likely not cover you. The personal insurance coverage you buy, will likely also not cover you.
2) If you get injured, you will not be eligible for worker's compensation.
3) You will be violating HIPAA by working off the clock - this could be termination offense.
4) You are letting your employer know that all the work they give you can be done in an 8 hour shift since you have clocked out after 8 hours and there is no record of overtime.