Stopping in Cold Spring is probably your best bet. It's about 10 minutes off the Taconic. In Cold Spring I'd recommend Le Bouchon or Cathryn's Tuscan Grill. Both are on Main Street in Cold Spring and about 10 minutes from Beacon. Here's my article on Le Bouchon.
In Garrison I'd recommend The Tavern at Highlands Country Club. I had dinner there on Saturday night and the food was very impressive. The Pork Confit was one of the best dishes I've had in the past 6 months. Also in Garrison is Valley Restaurant which is also exceptional but a little higher end. So take a look at the menu to see if it fits within your budget. Also double check that they serve lunch, I'm not sure if they do.
My last recommendation is further south called the Peekskill Brewery. They brew their own beer and have very good food to go with it. Their menu includes a lot of small plates as well which could be perfect for lunch. I had dinner here on Friday night and the braised pork belly was delicious. It's also less then a minute off route 9.
Hope this helps.
I recommend Poppy's. Definitely casual, but the burgers are amazing, and the chef/owner couldn't be nicer. Or if you go elsewhere, check out Zora Dora which is also on Main Street in Beacon. Homemade gourmet popsicles that are delicious and he's always coming up with new interesting flavors! I'm just not sure if he's open now that it's not warm weather anymore.
check this board, but poppy's burgers is organic fed. the thai place there is ok for up here, but *nothing* compared to manhattan.
there's also another organic burgers place in cornwall on hudson, whose name escapes me.
in beacon, on the corner of main and (near the train station) is a little ice cream place which serves jane's, which is local (to kingston).
if you want peruvian, cross the river to new windsor (machu picchu). fishkill has a decent cuban place, but i can't compare it to manhattan ones (babalu bob's).