An open container ticket is a Class C offense. This is the lowest offense in the state of Texas, it is like a speeding ticket. The max fine for the open container for the passenger is a fine of $200.00. There is no jail time possible unless he does not show up at court then he can be charged with failure to appear. Often times he can get a deferred which means stay out of trouble, no other tickets, etc. for a period of time (usually 90 days) and the ticket will be dismissed. Of course, if he did not have the open container in his possession then the officer must prove he had care, custody and control. Just because he was in the vehicle is not enough to prove possession.
Mr. Hamilton is correct about the level of charge, possible punishments, and the level of proof to satisfy the requirement of possession. If there were multiple empty cans in the vehicle, then frequently the officers give everyone a ticket for open container - even if there is just a drop left.
If he driving and only received a ticket for open container, he is blessed that he did not get a DWI (driving while intoxicated.) That may be what you are thinking of in Arkansas law (although I guess they could consider it a felony to have an open container.)
Your boyfriend should hire a lawyer that specializes in traffic court cases. Even though I have 21 years experience in criminal cases, I feel more comfortable referring out traffic court cases because the guys that go there day in and day out know the judges, know their rules, and can usually work out the best situation in the event your boyfriend changes his mind.
If your boyfriend does get a deferred and he successfully completes it, he then needs to take another step to get the case off his record. It would not look good in the future, particularly if he is ever suspected of driving while intoxicated. The police can see the results of traffic cases when they run record checks. Remind your boyfriend to talk to the lawyer about clearing up his record when the case is over.