Whenever possible try to find the required Thai ingredients. Most are readily available at Asian Markets in the US and the UK.

Substitutions if Needed

Shallots = red or spanish onions
Bamboo shoots you may use asparagus in stir fry dishes
Thai chiles = pkrik kee nu serranos
Thai chiles = phrik chi fa jalapeno
Thai Chile Powder = ground up dried chiles = Mew Mexico Chiles
Thai Chiles bottled chile sauce, ground dried chile, or dried chile flakes
Lemon Grass= Equal amount of grated lemon zest with a bit of fresh lemon juice
Dried red Thai Chile = Chi fa haeng = jalapenos
Coconut milk = milk or soy with coconut flavouring
Fermented fish = anchovy paste
Nam Pla = Fish Sauce = anchovies pureed with a little water
Fermented pork = pork, marinaded in lime juice
Lime juice = lemon juice (but lime is best)
Limes = lemons (but lime is best)
Gourd leaves (bai dumleung) = watercress
Phak kana = Thai kale = broccoli
Makheau phuang = Thai pea eggplants = garden peas
Green mangoes = green papaya or sour green cooking apples
Palm sugar = light brown sugar
Shrimp paste = anchovy paste
Thai basil = Bai horapha = a mixture of Italian basil and mint
Tamarind juice 5 parts tomato catsup to 1 part vinegar
Mooli (white radish) = turnip or daikon
Kaffir Lime Leaves = bai magroot- use citrus levaes or lime zest
Thai Eggplants size of golf ball-Asian eggplant cut up
Pomelo = Som 0 = Pink Grapefruit
Galangal = Kha = Young ginger
Phak bung = Swamp cabbage = cabbage leaves
Ba mei = yellow egg noodle = Italian spagetti
Wunsen = cellophane or bean thread noodle
Phak chi = whole coriander/cilantro plant incl. the root
Thai celery = chinese celery = western celery
Maggi seasoning = equal volumes Worcestershire sauce and dark soy sauce
Banana Leaves (as wrappers)= fresh corn husks, ti leaves, or parchment paper
Sweet Soy Sauce 1 part soy sauce to 2 parts palm sugar boiled until syrupy, then cooled
Bulls blood = heavy red wine