2. England's sweet and smoky HP Sauce is an ideal match for a steak sandwich. Its vinegar-chile notes and hint of dried fruit also make it perfect for roast pork.

3. The British anchovy paste known as gentleman's relish delivers potent depth to everything from roast beef sandwiches to buttered toast.

4. Punctuated with green chiles, cumin, and cilantro, schug is a fragrant Yemenite hot sauce that's added to shawarma, falafel, and hummus pitas.

5.Turmeric pickle, made with turmeric rhizomes, chiles, ginger, and lime juice, can lend texture and zing to Indian wraps, both vegetarian and meat-filled.

6. The ultrafiery Barbados Hot Yellow Pepper Sauce, made with mustard and Scotch bonnet chile, adds a capsaicin bite to the cutter, a Bajan fish sandwich.

7. Popular in Australia and New Zealand, Vegemite, a rich paste made from yeast extract, adds a distinct vegetal flavor to toast and butter or an avocado sandwich.

8. Chicago's Italian beef would be incomplete without giardiniera, a mix of pickled vegetables that includes cauliflower and olives.

9. A Polish blend of horseradish and sour cream, called sos chrzanowy, adds richness and heat to sandwiches with meat, fish, or eggs.

10. A drizzle of the MSG-rich Maggi Seasoning —a classic ingredient in the Vietnamese banh mi sandwich—imparts intense, meaty flavor.

11. The pickled mango condiment amba is part of Israel's melting-pot cuisine, introduced by Iraqi Jews. It's ladled on sabich, a pita stuffed with eggplant and hard-boiled eggs.

12. The most famous canvas for Cheez Whiz—spreadable cheese that becomes a sauce when warmed—is the Philly cheesesteak.

13. Favored by the French for its crunch and pungent bite, whole-grain Dion mustard delivers texture and spice to a sandwich.

14. The North African sweet-tangy salad of roasted pepper and tomato called mechwiya is delicious spread on flatbread sandwiches.

15. St. Hubert Sauce, a rich gravy, is a key ingredient in the hot chicken sandwich a jus-drenched specialty of the Quebecois chicken chain St. Hubert.

16. Sir Kensington's Gourmet Scooping Ketchup is hot-sweet, thanks to the addition of jalapeños and honey. Akin to cocktail sauce, it pairs well with a crab cake sandwich.

17. Japan's squeeze-bottle Kewpie mayonnaise has a unique richness and rice-vinegar tang that's ideal on vegetable sandwiches.

18. Tyler Kord, the chef at No. 7 Sub Shop in New York City, adds bursts of ripeness and acidity to his brie sandwich with pickled blueberries.

19. The british vegetable relish Branston Pickle completes a Ploughman's sandwich, along with cheese, butter, and crusty bread.

20. The yellow hue of the British relish piccalilli hints at the high mustard content, which makes it a sharp partner for mild deli meats such as boiled ham.

21. The North African hot sauce harissa, made with chiles and oil, is a beloved condiment in Morocco and Tunisia. Try it on a merguez sausage sandwich.

22. Red pepper, eggplant, chiles, and garlic comprise ajvar, the Balkan sauce (also eaten as a side dish) thats a potent addition to a cevapi (skinless sausage) sandwich.

23. An american cousin to British piccalilli, chow-chow is a green-tomato and mustard relish that's a zesty counterpoint to burgers, hot dogs, and other savory meats.

24. The syrupy, ketchup-based tonkatsu sauce, with hints of garlic and ginger, adds umami flavor to Japan's panko-breaded prok cutlet sandwich.