All occupations can be classified using the NOC, of course there is an NOC code for it - 6621
http://www5.hrsdc.gc.ca/noc/english/noc/2011/ProfileKeyword.aspx?val=6&val1=6621&val11=gas+bar+attendant&val12=0&val13=0&val14=&val15=0&val16=0
It doesn't "count" because it apparently was pre-graduation as well as unskilled. You do need to mention it in your Background Declaration, but not on the Schedule 8 - Economic class - Canadian Experience Class form. If this experience was in the past 3 years and you don't have a Letter of Employment, include a written statement saying that you don't have a Letter of Employment for this position because it was unskilled and pre-graduation...