1. stop doing something
pack in your job
To pack something in is to stop doing something or to quit. When you pack something in you give up or desist. This is an idiom that is used in both social and professional contexts.
2. fit a lot of things or people into a limited period of time or space
pack in a crowd
To pack something in can mean to fit many things into a small amount of space or time. Similar in meaning to 'squeeze in' or 'fit in'. So for example, if you go on holidays you might pack in a lot of activities.