While I haven't decided what exact medium I will use, markers seem like a good candidate. Especially material markers, like these sharpies, in bright colors.
DIY gift bag - "Stained by Sharpie" fabric markers - How About Orange
9 Things You Need before Starting to Fabric Paint: Optional: Fabric Marker Pens
Watercolor floral pattern lesson - painting with watercolors on fabric opening craft
Bleach gel in bottle (not a pen) creates a loose drawing, then tighten it up w/ fabric markers 4 fun technique - BACK
Citrus Stamped Tea Towels - gifts for the homebound
Multi Fine Primary 6pk $6.99
Adult coloring - use fabric markers on this DIY tea towel to make a colorful unique gift!
One comment suggested giving guests/kids fabric markers to decorate. Another suggested using a second sheet to cover the food.
5 Ways to Use a Fabric Marker or Fabric Paint Pen: Stamping with a Fabric Marker