Buy pad thai sauce, or make your own. Pour vegetable oil in an 8- to 10-inch frying pan over medium heat. When hot, add shallots and garlic and stir until limp, 3 to 4 minutes. Stir in tamarind concentrate (or substitute 1 tablespoon dark molasses and increase lime juice to 1/4 cup), brown sugar, Asian fish sauce, chili powder, and lime juice; cook 1 minute. Let cool; chill airtight up to 1 week.
Seal carrots, bean sprouts, cilantro, green onions, and peanuts in separate plastic bags; chill vegetables and cilantro.
Purchase rice noodles, lime, and shrimp (pack frozen) or tofu (cut into 1-in. chunks; seal in a bag and chill).
Pack a large pan; a pasta insert or a strainer; a medium pan for sauce; and tongs for combining noodles and sauce.
Halve and slice lime.
In a large pan over high heat, bring 3 quarts of water to a boil. Add noodles and cook until barely tender to bite, 3 to 4 minutes. Drain noodles and rinse well in cool water. Return noodles to pan.
In a medium pan over high heat, heat sauce and shrimp or tofu. Add to noodles with carrots, sprouts, cilantro, green onions, and peanuts; mix to coat. Accompany with lime slices.