Hi Chris,
There are a lot of day trips in BKK, just to name a few good ones that i have been:
1) Safari World-Great place for children with the safari park tour and a lot of animal shows. Also lunch included. A 9 till 5 thing.
2) Bang-Pa-In Palace & Ayutthaya (Unesco Heritage)-You trip will travel by coach while going to the places and back on cruise coming down from Chao Praya River, also lunch on board.
3) The Bridge Over The River Kwai, Kancanaburi.
4) The Grand Palace.
5) Chatuchak Market, prepare to get lost.
For the above, just google to find out more.
Food wise, BKK is always great. Yaowarat (Chinatown) always good to be there for dinner especially for hawker food and seafood restaurant. Nam Seng at Soi Texas is good.
Another place for dinner and enjoy the back nite view will be Crystal Grill at Baiyoke Skyhotel, Pratunam. Their buffet on the 82nd floor~uhmmm,so great!. Also, one must try their 360 degrees revolving roof deck and you can see the whole of Bangkok.
For watches only 1 place Siam Paragon, i personal favourite will be Trocadero (distributor/retailer for brands like Seiko (Credor, Galante, Credor, Ananta) and Orient.
At Siam Paragon, there have a high-end supermarket Market Hall and be amaze with their grocery assortment (just compare with BIG at Publika). There have one of the biggest non-halal corner.
Maybe can go for a movie and feel the Thai citizen rise for their national anthem (include non Thai) that our country just borrow that idea recently.
You will be simply amaze with the citizen loyalty to their country as their national anthem in play twice in a day at 8am and 6 pm. At sky train stations, in parks, in shopping malls and in government buildings all over Thailand, you will see people stop what they're doing and stand to attention.
Have a nice trip and simply be "Amazing Thailand".