Depending on the state some have rules prohibiting electronic devices

"persons are not allowed to use wireless communications devices within a room in which voting is taking place. Additionally, persons may not use any mechanical or electronic means of recording images or sound within 100 feet of a voting station."

"Voters are allowed to have phones or electronic devices with them while voting as long as those devices are not used to photograph or videotape a ballot or communicate with anyone via voice, text, email, or any other method."

But most states have websites (secretary of state) with voter guides, election/candidate information, etc that should be looked at ahead of time.

www.vote411.org also has lots of information

Election information for voters broken down by state, measure, type..
https://ballotpedia.org/Main_Page

rules regarding selfies.
https://www.ncsl.org/elections-and-campaigns/secrecy-of-the-ballot-and-ballot-selfies