Jobs

Well i never thought i'd be in a situation like this. I have a dilemma...well it's not a dilemma yet, here's the problem, u remember the volunteer job i told u about at the vet clinic, well that's about a 95% guaranteed position but its volunteer so i wouldn't be making any money, however Kroger called yesterday and offered me an interview when i get back down to Cincy, and i know an interview isn't a job 

BUT lets say i get the job, do i take it and end up bagging groceries for a paycheck 
 OR do i turn it down for a chance to work at a vet clinic with no paycheck but a more career-suited kind of experience? I don't think i can do/handle both and im not really going to try cuz i need to focus on school. 

I'm going to the interview, that much i know but i told the doc id volunteer first, i just dont know what i should do if i get both, i know the money is what i need but i also know id hate bagging groceries, which is what the interview is for. I was thinking id go talk to the vet and maybe see if i could just volunteer during the weekends and then maybe only work at Kroger during the week. 

My problem with that is i really need to get better grades this quarter, especially with 4 of my 5 classes being academic classes, im not worried about math but i need a 'B' or better in both bio and chem.

SO do i go for the money or for the experience?