That's a really pretty time of the year to be in the finger lakes region. Since Trumansburg is near Cayuga Lake I will stick to just giving you suggestions of places to visit that are surrounding that Lake.
You'll be near Taughannock Falls so I would suggest at least stopping by for an hour or two.
Taughannock Falls State Park - NYS Parks, Recreation & Historic Preservation
One of the things I like to do is start driving along the roads that go around the Lake. You'll see signs all over the place for the wineries
Home - Cayuga Wine Trail and you can stop at how ever many you want. There are also a lot of Amish along that route so you will probably see horse and buggy while driving along and there are several one room school house's for Amish children. Although the Amish in this region aren't really a tourist trap like Lancaster PA so it's seeing them more in passing. But they will often have roadside markets that you can stop at.
Along that route is also Aurora NY. Aurora NY is on the other side of Cayuga Lake from Trumansburg and has the famous Mackenzie Childs
MacKenzie-Childs - MacKenzie-Childs - Hand painted ceramics, dinnerware, tableware, glassware and home furniture and I like the Pumpkin Hill Bistro in Aurora for lunch.
Pumpkin Hill but a lot of the wineries also have excellent restaurants.
Seneca Falls is on the same side of the Lake as Trumansburg.
Seneca Falls, NY - Historic Gateway to the Finger Lakes This has the Womens Rights National park and museum
Womens Rights National Historical Park - Women's Rights National Historical Park and Seneca Falls is highly believed to be the inspiration for Bedford Falls in It's A Wonderful Life. So Seneca Falls does a lot of things related to that movie.
Ithaca NY is also really nice and Cornell University has several places that visitors can enjoy. Ithaca has the famous Moosewood Restaurant
Moosewood Cooks | Vegetarian Recipes & Restaurant | Based in Ithaca, NY | Moosewood Restaurant Cookbooks There is the Cornell plantations and you can go to their Botanical garden and arboretum
Our Gardens & Natural Areas | Cornell Plantations and Cornell Ornithology Lab
Visit the Lab, Hours, Directions, Sapsucker Woods Cornell is an Ivy league school and has a beautiful campus. There is also Lucifer Falls
Robert Treman State Park & Lucifer Falls Waterfalls Information
A couple of things not far from Cayuga Lake but not right on the lake are
The Harriet Tubman Home - Underground Railroad
Harriet Tubman Home, Inc. | Home
Corning Museum of Glass -
Corning Museum of Glass
Watkins Glen - NASCAR
Watkins Glen International - Watkins Glen International
Elmira - Mark Twain summer home (where he wrote most of his books) and grave-site
Mark Twain Country
Skaneateles - Beautiful old town with lots of little shops on the Main street
http://www.skaneateles.com/
Apple picking is usually a really big thing in this region but because of the freeze that occurred in the Spring I'm not too sure how many Orchards will be open to picking this fall. But the Lafayette Apple festival is that first week in October
LaFayette Apple Festival