We have a Nabi Jr. and it is great. Drop it, shake it, whatever - it's a durable little thing with lots of educational games on it. But for the lines, we didn't need too much for the babe. Snacks are good - especially the squeeze pouches. But sometimes he would just hold his little hand up and push the pouch away. Graham crackers and M&Ms are winners, but then you wind up with a sugar rush kid. Bring the little water sippy cup, especially one that is leak proof. That is the best as well.
Also (and I hate saying this) bring a leash. The monkey backpack one is great. That way, if you get tired of holding the kid, you can at least put them down for a bit and they won't get away from you! I was opposed to leashes before boy was born, but I am so thankful now because boy is a runner and likes to be on the ground.
Overall, the lines are so freakin' exciting for a two year old - even if it's a brick wall - that we really didn't need much. Boy was excited about the texture of the walls, the anticipation of the ride, the music, etc - being bored wasn't an issue.