Passport protection the less glamours side of travel.

re-sealable plastic bag.... like the sandwich size version of the 3-1-1 bag

There are any number of passport "wallets" that should do the job. Or you can simply put it in a small freezer type zip lock bag.

I use the small "snack-size" ziplock bags for my passport when stashed in a money belt or sometimes even in my purse if it's rainy. It doesn't close all the way but it's enough of a barrier to keep my passport dry and non-sweaty.

The last few trips I've used very little actual cash. I'll probably always have 50-75 whatevers but I just got home Thursday from the Scottish Islands of Orkney and Shetland and the ONLY cash I used was to buy a bottle of water one time to get some pound coins to leave as tips for housekeeping. I used ApplePay almost exclusively including at 2 small local textile crafts stores on Shetland.

The RS neck wallet seems to have a pretty good vapor barrier between my passport and my sometimes damp undershirt. With a previous (inferior non-RS) wallet I used to wrap the passport in a plastic sandwich bag, but I haven't bothered with that in awhile. Spring and fall travel helps, vs. summer.

The backup cash is usually in a pocket of the neck wallet in front of the passport, so away from sweaty me. And how wet can it get, really, before I've spent it?

I switched to the hidden pocket that hangs from your belt. I keep it on my side close to my hip. That area is much less sweaty than the area below my abdomen. When I wore the money belt and inserted a ziplock bag inside I retained a lot of heat and moisture in that area. Hidden pocket is much more comfortable for me. Still use the ziplock bag inside it.

ankle wallet for passport. Can get online or REI. Use a coin purse for what little cash you might need.

Front pocket of my jeans

I use a hidden pocket and moisture has never been an issue.

My daughter came up with a great solution one summer when we were traveling to Rome. We took several sheets of the 'select a size' paper towels. We took the small size and folded it and placed between plastic and interior side of the money belt which is next to your skin. The paper towel soaked up any moisture. I always do that now. In fact, paper towels come in so handy I carry a few sheets when I travel any time of year. They really take up no room and weigh practically nothing.

A ziplock bag for the passport and cash. Then it doesn’t matter how much I sweat.

douglas,

I've been placing my Passport inside a small zip-lok bag whenever it's in the money belt. I've never had any problems with that method, even in extremely warm weather and lots of perspiration. I sometimes have to sink-wash the money belt during trips, but that's easy and it dries quickly.

I don't keep my passport on me most of the time. On our most recent trip, the only times I kept it in my pack on me was when we left our camper for longer hikes, 10 and 12 miles. Within my pack, I just toss that, my credit cards and a bit of cash into a ziplock and call it good.

I loathe money-belts/neck wallets unless i'm carrying a significant amount, I just find them uncomfortable and impractical.

My pants have a couple of hidden zippered-pockets, I keep my valuables there. When I've settled into my hotel/rental, I'll carry a copy of my passport instead and leave the real one behind.

True about the neck pouch in that regard in hot and sticky weather. I wear it anyway. No problem wearing the hidden pocket.

I use a hidden pocket and moisture has never been an issue.

I'd like to change my answer please. Just back from Washington DC and Baltimore and sweated buckets. I use a hidden pocket and my passport and cash were damp. I wouldn't be overly concerned except for the report that the latest generation of Canadian and Australian passports aren't holding up well when moisture is added. https://www.ctvnews.ca/canada/canadian-government-admits-new-passports-susceptible-to-curling-1.6537878#:~:text=The%20curling%20of%20the%20cover,acceptable%20for%20an%20official%20document.