It's difficult dealing with so many different currencies when traveling. At the end of my stay, I always have some residual amount left over. What to do with it is the question.
I try to minimize it by taking out just enough that I'll use. But I also like to take out as much as possible each ATM withdraw because it's less expensive that way with the fixed fees charged. Regardless, I'm left dealing with left over currency.
My options include:
Exchanging back to US dollars. Be prepared to lose 10%
If I'm not using points for my hotel stay, partial pay with cash.
Use to pay my taxi ride to airport
Give generous tips the last day
Seek out the homeless and hand over cash
Keep it if I think I'll return one day
I've used all these methods in the past. But I'm still stuck with a bunch of currencies from various countries I have stashed in my backpack. I really don't know how much it is but likely a few hundred dollars in US equivalent currency. Not a big deal.
But it is important to be vigilant over the years because this can turn to thousands with my amount of travel. Recoverable, but can be a pain in the butt.
But the bigger issue I have with foreign currency is getting used to it. The coins? Forget about it! I never know what they're worth. I'm at the mercy of the vendor to tell me. I think they're mostly honest but im not sure. Besides, it's just change.
The bills also can be confusing. It's very easy to make a mistake. I'm constantly doing the conversion to US dollars in my head to make sure I'm not overpaying. Even then, it's easy to make a mistake getting the denominations mixed up,
On a trip to the Philippines I took a taxi ride. Taxis are cheap there (if you don't make a mistake). At the end of the ride the meter (yes, sometimes they actually do use meters) read 270 PhP (Philippine Pesos). That's about $5.00. But I handed him 3,000 pesos for a whopping $50.00+. Instead of handing him three 100 peso bills I gave him three 1,000 peso bills. To him that was as much money as he nets in probably 4 days of taxi driving.
He looked surprised when I handed it to him but I thought because he was appreciative of a 10% tip. But he never corrected me. It wasn't until later I realized my error.
It's hard to know how many times I've done this and not caught the error later. Currencies can be confusing with it all looking so, well, foreign.
In the USA I rarely use cash. I might use $50 in cash every month. I use credit cards for everything unless it's not accepted. I do the same overseas as much as possible, however, the places I go it is more likely cash only is accepted. You need to carry local currency.
I expect as I continue to age and math gets harder to do in my head, I'll lose more due to faulty currency exchange. If only my pride would allow me to use a calculator. But im unsure that would matter in many cases.