Printfile makes negative sleeves that are designed to hold both the film and a contact sheet. I don't use them for that...but I do use them to obtain perfectly-aligned proofsheets! Just slip your unexposed paper into the large sleeve designed to hold the proofsheet, so that the emulsion side of the paper faces the emulsion side of the film strips. Place on the baseboard, put a piece of glass over it, and turn on your enlarger! It is one of the coolest printing tricks I have ever discovered. Saves soooooo much aggravation (and materials, even).