Here is a mini succulent terrarium made with a round glass bowl. Maybe the same idea could be used with your glass loaf dishes, using one for the bottom, and one for the top, so that the contents are entirely enclosed?
I would put sand and pea gravel (for drainage) on the bottom, followed by potting soil and plant herbs for a kitchen garden.
You can use them to make me a few loaves of banana bread. You could always use them in a storage solution. Place them some place and add small items. Sort of like a junk drawer, but more organized.
Use them for a succulent garden !
An herb garden would be cute too. How fun!
Bake something in them and give as a gift.