Actually a S rank adventurer could enjoy a lot of benefits. In any nation they were treated akin to royalty. Elena was able to book the special VIP room using this privilege. This room was very luxurious even compared to the normal VIP room.
But the food and drink counters were not present inside as not to affect the luxurious decor of this room. That was why Nina had to go out earlier to the regular VIP rooms to get some staff to eat and drink. And that's where she was able to spot the students and bring them back with her.