It might be a little too late, but I grew up in Kissimmee and still have family there. Not sure where you are staying, but there are a couple of great places right in downtown Kissimmmee.
Broadway Pizza - Great pizza place with a bar.
3 Sisters Speakeasy - Has good bar food/sandwiches/entrees. Plus, you can order in sushi from the place next door.
Sushi - Next door to above, great as well
There is another place nextdoor to that as well but I have not eaten there.
On weekends, all the places open up to eachother and you can order stuff from each place from your table. There is usually some type of live music, and a couple of great bars right there as well.
Vintage Vino has a huge wine selection as well as many craft beers.
If your more towards St. Cloud, try the clubhouse at the St. Cloud Royal Links Golf Club. Great food as well.
There are also all the usual chain places, but you can get that stuff anywhere.
I'm sure there are a lot more, but we usually tended to stay away from the stuff west of John Young (on 192) as they catered to the "one visit tourists", and the food and service was usually sub par.