^^^^. Not at all foolish to keep small amounts of local currencies when one travels in and out frequently. I appreciate having no need to make the ATM the first stop on arrival after an 8 - 17 hour flight. No concern as to whether or not my taxi driver will take my CC when I know I'm carrying sufficient cash if required. My "cash stash" tends to arrive and leave pretty much in tact for many locations as CC is my primary method of payment. I have been in situations where electric was down and cash was required in normally "cashless" situations. Glad for the stash.

I have Euros and Hong Kong presently. Just found a 5 pound note that I will use next month. I don't typically keep UK currency after making a trip to the Bank of England las fall to exchange some just expired bills. Spent down the Singapore cash to zero as those trips ended. Same with Canadian.

I like to keep the small coin of the country I've come.

I still have the coin of Singapore, Thailand, Japan, Malaysia and China. It's nice to keep them to memorize about my trip.

I don't keep but use USD cash because it's the most accepted currency and furthermore the exchange rate in other countries, especially Asia is stronger in relations to normal exchange rates in banks in North America and EU.

I have leftover cash in various amounts for countries I expect to be visiting again in the near-medium term:

Canada (also have bank accounts there), Mexico, Israel, Taiwan, euros, Brazil, Uruguay... Have some stray British coins I figure I'll use at some point as well.

I keep basically every foreign currency leftover after a trip, and usually hit the ATM for $100-500 in local currency anywhere I'm staying. I keep it in safe or safe deposit box and take whatever I'll need for each trip. I have about 30 currencies and amounts ranging from USD 5 to USD 5000 of each. USD, EUR, GBP, CHF are my "focus currencies", though. I have ~5k in RMB and 4k in THB which is pretty inconvenient.

No interest earned, but it's sort of a hedge, and mostly a convenience thing. Depending on the country, cash notes can get discounts bigger than credit card benefits.

I have South African rand since we go there often, Aussie dollars, and euros. I just found some Hong Kong dollars that we will probably never use.

Euros and GBP are the top ones I keep. But really, I'll keep anything that isn't worth exchanging because its not a high enough value.

Well, I keep small amount (like less than $10) of foreign currency from most counties I've visited - consider it a hobby.

In addition to Singapore dollars (primary currency), I have all currencies in the SEA country region except Philippines. List of currencies include Bhutanese ngultrum, Euro, Swiss francs, USD, AU and NZ $, Russian ruble, Georgian lari, Azeri manat, Turikish lira, South African rand, Mexican and Australian pesos, Brazilian real.

That's it so far...

A debit card via a local ATM is indeed how I get the local currency in the first place.

For me, the difference is whether I try to spend down the local currency before I leave (home being the US) -- the two that I don't spend down are Canadian dollars and euros, because I go frequently enough that I like not having to go to an ATM first thing upon arrival. Before leaving the foreign country to come home, if my cash reserve is less than CA$100 / €100, I'll make a stop at a local ATM and "top off" the cash so that I leave the country with that amount of cash.

(It is true that in Canada and France, which is the eurozone country I visit the most often, credit cards are accepted pretty universally, but in places like bars or outdoor markets it's often easier to pay in cash.)

All other foreign currencies I try to spend down before I leave, because I travel elsewhere infrequently enough that I don't mind going out of my way to find an ATM upon arrival.

I usually try to use up whatever leftover currency I have unless I know it's some place where I'm highly likely to be back within a year (JPY, EUR, GBP, SGD). That also guides my ATM/exchanging habit as I don't want to "have to" exchange things back or spend at the airport.

A couple of times, I've had more of something than I planned on using in the near future and figured I'd just exchange it for something on the next trip versus exchanging back into USD.

It can be helpful to carry a bit of cash on hand if the local ATMs or card payment infrastructure is down. e.g. I was passing through AMS and the bus ticket machine wasn't reading my card correctly, so having 10� on hand to cover the bus fare was helpful in this regard.

Personally, I have a small stash of EUR and some CAD/HKD since I visit those most frequently.

Currently only have a few GBP and Euros.

Anything left over from 70-plus countries, even currencies no longer in use. Last year I eschewed my old bag-of-everything in favor of country-specific 6.5"-by-3.5" envelopes. Obsolete money is a nice souvenir. In-use money goes in its envelope with transit cards, so when I head to Hong Kong I just pull that sleeve and I've got cash and my Octopus card.

USD, Euros and GBP. I use my cards in most of the places I visit regularly. Sweden and Denmark are trending to cashless

NTD, HKD and USD.