Hi, S. Jackson,
Callendar House, right in the middle of Falkirk, has an excellent tea room, which serves hot meals and sandwiches throughout the day. The food is inexpensive, and admission to the house is free.
Callendar house is a 19th. century chateau, built around a 14th. century tower house, which has been well preserved. There are extensive grounds, and the interior of the house is beautiful. If you're interested at all in Roman history, part of the Antonine Wall runs through the Callendar House grounds. Famous guests have included Mary, Queen of Scots (Is she dead yet? No I'm not!), Bonnie Prince Charlie, and Queen Victoria.
If you're driving, there is free parking at the edge of the grounds, just off of Kemper Avenue. If you're not driving, the number 3 bus runs between the Kelpies and the Wheel. Callendar House is walking distance from the Falkirk High train station, but you'd need a bus or taxi to get to the Kelpies and the Wheel if you're using public transportation.
If you're an "Outlander" fan, the kitchen of the Callendar House was used as the Duke of Sandringham's kitchen, where Murtagh cut off the Duke's head.
You can get 90 minutes free parking in the ASDA car park if you make a purchase. The car park on the other side of Glebe Street is free after 3:00 p.m.
p.s.: If you're planning to overnight in Falkirk, and are looking for an inexpensive place to stay, I highly recommend the Premier Inn Camelon. It's right on the bank of the Forth & Clyde Canal, and about a 15 minute walk along the towpath to the Wheel. If you get a room in the back of the hotel, you may get to see the locks opening and the houseboats going through. Rooms are very cheap at this time of year.