My summer experiences were pretty varied. I also had a lot of research experience left over from summers during college, including a third author pub.
I worked as an animal care tech for the teaching a research animals during school (on weekends) and for one summer. Horses, pigs, goats, rodents, dogs, everything. Basic feeding and cleaning but I got to get involved in some research projects - path looooves research.
Next summer I did an externship at the Wake Forest pathology program with their primates. I can give you contacts for that if you would like. Also check out
www.acvp.org - they have a nice listing of programs that advertise summer externships.
http://www.acvp.org/educators/Externship.cfm
Next summer I did an NIH-funded research project (you'll hear about it at VMRCVM - definitely try to do it). And throughout second and third year I also did the clin-path job.
In addition, I took multiple advanced pathology courses and got a few good path rotations at various places for my elective blocks. I especially recommend Purdue - I had a great time there.
I don't think working during school is absolutely necessary. I assume you are P/C track? If so, you'd have more time to do it than, say, an Eq tracker, but it's not everyone's cup of tea. Yes, I do think summer and break experiences plus excelletn LORs would be ok with no during-the-semester experience, because they know some people can swing working PT and some cannot.
And something I realize I may have glossed over - my acceptance into this program with my GPA is the exception, not the rule. Path DOES tend to be more forgiving, but you'd better have a helluva lot of experiences and good LORs to balance it if you have/had my GPA. Because although it is not the most important thing, it IS still an issue.