I'll pay for friends all the time and in turn the next time we eat or go drinking, they'll return the favor. Don't worry about things like these so much, life is too short. Not everything has to mean something.
I think the drive to Austin puts you in a committed relationship. Who pays for lunch is just one of the cute things some couples stress over early on.
"Oooh, yea! I think I'll try it too! ...I'll be right back, need to use the restroom." how did she say the "oooh yea" part? was the Oooh part emphasized? If so, I think that's a clear signal that she wants to take things to the next level. But if the "yea" part was emphasized, then you're only a friend so far. Now, the kicker is the "I think I'll try it too!" Did she really sound excited enough to put an exclamation mark? Think hard about it. You don't want to misconstrue her intention of taking things slowly or you could really screw things up. The "I think I'll try it too" is a double entendre. Because it was followed by "I'll be right back", it means she'll always come back to you. She feels you will never let her down. The "need to use the restroom" part is because she needs to pee.
You should have paid for it, then when she came back say to her, "I went ahead and paid for yours. You owe me so and so or I'm going to punch you in the face."
