  ooooh. its a toughy. you see it depends what mood your in doesnt it? sometimes its just gotta be peanut butter and jam (sunpat creamy crunch with robinsons strawberry). but then theres equally a time for the classic cheese and pickled onion. in my meaty days i used to like corned beef and brown sauce (HPs) or a salami/pastrami choice if available from a take out place. increasingly im favouring philedelphia cream cheese on plain white, to take to work, wrapped in foil. must give some respect though to the mighty Subway. the fastest growing convenience food/retail outlet in western europe. healthy. reasonably priced. good selection of breads and filling. if you can find a store that has cream cheese (i know of only one and am keeping it secret), then try that with a selection of pickles, onion and honey mustard sauce on italian bread. mmm mmm. 
