At home: Dice the pineapple, onion, and jalapeño. Chop the cilantro. Squeeze the lime juice into a small leak-proof bottle. Pack each ingredient in separate small containers or zip-top bags and store in the cooler.
At camp: Combine the pineapple, red onion, jalapeño, and cilantro in a medium bowl or wide-mouth jar.
Add the lime juice and salt. Stir gently to combine. Taste and add a pinch of sugar if the pineapple is not sweet enough.
Let the salsa rest for 5 minutes at room temperature so the flavors meld. Serve immediately with tortilla chips, on grilled fish tacos, or alongside any campfire-grilled meat.
Storage: Keep any leftovers in a sealed container in the cooler. Use within 24 hours for best texture and flavor.