Should I quit?

As the title implies, I'm considering quitting my job. I (20m) have worked in a grocery store for 4 years now. This place has gone to hell in a handbasket over the past year. I thought it would get better eventually, but it just keeps getting worse. I am given management duties on the front end (regusters, self checkout, togo, cash office, etc) without management pay, I get full time hours with this part time job, half of my coworkers and managers don't actually do their jobs, and I have to pick up their slack most of the time. I am constantly abused by customers, management tosses me around because I'm good at my job, and I come home completely drained and exhausted every day due to the stress. Recently, I had a customer make a threat toward me. I told the store manager, he asked me for some more details, and he said he'd look into it and told me not to hesitate to call the police. This is probably the straw that broke the camel's back because this job already stresses me out enough. I don't have another job lined up, but I'm financially stable enough to not have a job for a couple months since I still live my parents and I'm in school. My parents and even my grandparents have agreed that it may be time for me to leave this place for good. I will continue to look for a new job because I don't want to be unemployed for long. So, based on this info, should I quit?