aaaarrrr depending on how big the event is, your mobility company may be able to deploy a microcell. that's probably the most hands off way to handle it, but also probably the most expensive and least likely to actually happen.
Depending on your skill level: you could use a satellite Internet connection with a local mesh network (or even just a single outdoor AP depending on how much ground you have to cover). Staff would then use wifi and you could use something like discord or a local SIP server to facilitate VOIP calls between staff members.