If you are told "bring your own sanitizer" to an event what do you do?

First of all, there are two kinds of surfaces: Hard and Porous.

Hard surfaces are plastic and metal. 

Porous surfaces are fabric, wood, and foam microphone covers. 

Hard surfaces like radios, electronics. and some car parts are sensitive to corrosion which can be caused by chlorine based products so it is safer to use alcohol or hydrogen peroxide based products.  

You can make your own sanitizer using a blend of 50% isopropyl alcohol and water in a spray bottle. Spray that on to a microfiber cloth and use the wet part of the cloth to wipe down  your radio, headset and any buttons or other surfaces you are touching.

For porous surfaces that you can put in a washing machine, do that.

For a flag stick, you could wash in soap and water.

For those windscreens that go over the end of a microphone, you may be able to remove them and then rinse in soap and water and allow to dry before replacing them.

I always carry extra windscreens  with me for my own headsets. I wash them at home and carry them in a plastic bag to the place I will be working. Windscreens can be found inexpensively on E bay and Amazon in various sizes and shapes. 

For other porous surfaces like the inside of a helmet, you will need to use a different method like hydrogen peroxide vapor. Not something you can do on your own, so the facility providing the helmet should have access to this sanitizing method if helmets are shared. 

Here is a link to CDC list of approved disinfectants: https://www.epa.gov/pesticide-registration/list-n-disinfectants-use-against-sars-cov-2