Creating a bin or backpack make take effort at first, but worth it to have a ready-to-go tool for working a booth or event. Store one or more packs at a central location, or create your own if you work solo.
Clipboard for recording event, Master Gardener info, and number of public contacts
Clipboard with sign-up sheet for County Master Gardener Mailing List, if you have one
General supplies, such as pencils, pens, paper, tape, weights, etc
iPads loaded with University and other research-based links to plant, insect & disease ID databases. This does require web connectivity.
If you can't use iPads, consider plant, weed, and insect ID books
Adapted from Master Gardener Volunteer Sue Sherek in Anoka County, where they staff a couple hundred booths every year. Anoka volunteers keep their "Grab'nGo" backpacks at “Volunteer Central,” along with banners, props, and additional handouts and supplies.