If you’re taking a camera or binoculars, a brush is a must to remove grit from your camera sensor or eyepiece. I’ve learnt the hard way that even the smallest particles can ruin your pictures, and they can create permanent scratches if not removed. Once your camera is grit-free, use a small cloth to remove the dust that builds up underneath.
If you have your own wetsuit, make sure it dries thoroughly in the sun, then brush off all of the sand and salt so it doesn’t corrode the fabric, and wipe down with a wet cloth to remove any residue. Wetsuits aren’t that easy to repair due to the thick neoprene fabric so damage prevention is key.
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For more complicated repairs, I recommend finding a local tradesperson. In Australia, I took my camera, with a shutter that was stuck half-open, into a specialist store. The owner quickly fixed it as he had the right tool for the job (and in that case, he didn’t even charge me). You may be surprised at the things that can be fixed if you ask around in a market or shopping center.
And ultimately, there’s something so satisfying about repairing something on the road instead of throwing it out and consigning it to a landfill, and this is particularly important in places without robust recycling or waste collections. And you only need to pack a few small items (some of which you might have been taking anyway), and know how to use them, to play your part.