things to do at least once in Texas...
take a picture in the bluebonnets - do not pick them however!
drive to Galveston, watch the sunrise from the piers and then drive home
spend a day in Fredericksburg, then the next day go to Luckenbach

yes in that order...
take 635 around Dallas, cut through on 35 down to 20 then back up 45 onto 75 and back again - you will be a skilled driver after that
hail a cab anywhere in the state - I always SEE them but I've never seen anyone IN them
hop on into North by Northgate early, then roll into Deep Ellum all in the same night - after this try to find your way back up 35 northbound to Denton...
Chilifest
go to a concert at Billy Bob's
hmmm.....thats all I can come up with right now....feel free to add some!