When I would do mandala offerings I would think about the samsaric things I wanted and enjoyed then compared them with liberation for myself and others. Bodhicitta was more important, so I offer those things up. I'M OVER THIS JUNK! I WANT LIBERATION MORE! lol
Awacs, the trick to offering cake is making extra cake and offering the prettiest piece so you feel like you've given up a little attachment even though you haven't because ugly cake still tastes good.