For making Thai, Malaysian, Singaporean, or Indonesian noodle dishes:
Thai fish sauce (Tiparos or Squid brand)
Tamarind paste (Tamicon or Cock Brand)
Kecap manis (ABC brand) — Indonesian sweet soy
Sambal oelek (Huy Fong) — chili paste
Red curry paste (Mae Ploy) — for laksa, Thai curries
Coconut milk (Aroy-D, Chaokoh) — full-fat
Palm sugar — for pad thai, Thai desserts
Dark soy sauce — for pad see ew, char kway teow
Oyster sauce (Lee Kum Kee) — for stir-fries
Galangal (frozen) — Thai ginger relative; for laksa, soups
The picks above cover items 1-6 — the essentials. Add palm sugar, dark soy, oyster sauce, and galangal as you cook more SE Asian.
Thai vs Vietnamese Fish Sauce — They're Different
A common confusion: Thai fish sauce (nam pla) is sweeter and more aggressive. Vietnamese fish sauce (nước mắm) is cleaner and lighter. For Thai recipes, use Thai. For Vietnamese, use Vietnamese. They're not interchangeable despite both being "fish sauce."
If you can only have one bottle, Vietnamese fish sauce (Red Boat) works for both. Thai fish sauce in Vietnamese recipes throws off the balance more than the reverse.
Kecap Manis Has No Substitute
Indonesian sweet soy sauce is caramel-thick, syrupy-sweet, and uniquely Indonesian. No other Asian condiment is similar. If a recipe calls for kecap manis, you need actual kecap manis — Chinese sweet soy + sugar won't do it. ABC brand is the standard.
What to Skip
Generic "Asian fish sauce" without country specification — usually low quality
Pre-mixed pad thai/laksa sauces at chain supermarkets — usually corn-syrup-heavy
Light coconut milk in cans — full-fat is non-negotiable for laksa