If you're staying at one of Bangkok's many five-star establishments like the banyan tree bangkok, novotel chain of hotels. marriott, Amari Hotels and more, expect to tip the porter 20 to 50 baht, depending on how many bags you have but if you are an el cheapo, then just get your bags inside your room by yourself hehehe (that is if your bag has four trolly wheels as to make it easier to tug it along)
Fondest memory: tipping in bangkom is relatively cheap and the porters rarely complai if you give them small change as tipping is not a mandatory practice in thailand.
Favorite thing: You are not obliged to tip, personally I tip taxi drivers if I feel they have been helpful, 50 Baht is adequate. The only times I have tipped at a hotel has been for room service or the bellboy, again a small tip is adequate, 20 Baht for the bellboy. Just remember you are not obliged to tip, Thais very rarely tip.
Everything goes in Thailand's capital, and that rule applies to tipping as well. Some places expect it; others don't. In general, the more Westernized the place is the more likely you'll be expected to leave a gratuity.
Restaurants: Some top-end eateries will add a 10% service charge to the bill. If not, waiters will appreciate you tacking on the 10% yourself. However, if you're eating at a down-scale restaurant a tip is not necessary.