As a general rule, a GPA of 3.0 or above could be listed. If your GPA in your major is considerably higher than your overall average, you may wish to state it as well. Deciding to mention or not to mention your GPA is your choice. A young student with little or no relevant work experience may think listing part-time jobs or volunteer work is not important, but it is. Since many students graduating from college do have limited work experiences, employers are more concerned with the kind of knowledge, skills and abilities acquired from your employment.
Employment deals with problem solving, accomplishments and results.
As you write, think of why you were proud of your work experience. Do not underestimate the value of such jobs as wait staff, sales clerk or cashier. You have developed many transferable skills such as organization, verbal communication, working under pressure, customer service, etc. Descriptions of experience should include specific duties, accomplishments and achievements. The manner in which you state the skills you have developed, as well as your accomplishments, is very important.