I travel for half year every winter to south / central america from Europe, and there have been cases when my bank cancelled my credit card because of technical problems with contactless payments even though I didn't need contactless.
Another time Revolut just blocked my access to their app for a few days until I could prove where I got the money from.
Another time a bank blocked my card because I was travelling and they thought it's a fraud.
Depending on banks for long travels far from my home is scary, so I make sure I always have enough BTC and cash to survive.
I would carry 500-1000 USD at most.
When carrying €10,000 or more into or out of the European Union, you must complete a cash declaration. In practice, I'd feel uncomfortable carrying more than I'd be happy to count while hurrying for a plane, especially if the value were close to the limit and in a currency other than Euros. (Other currencies are explicitly included in the EU rules, which makes sense, not least because some EU member states use other currencies instead of Euros.) I don't know whether you can complete a cash declaration in case the exchange rate changes such that the value of your cash crosses the threshold, but if you can't then maybe carrying cash close to the limit would attract a lot of attention from customs or airport security (because it might look like you're violating the rules until the cash had been counted and the interest rate checked).
This is not true, you can carry 10000 EUR without declaration, you just neet to declare if you carry more (I look at the regulation and of course eurusd before I start my travel for winter).
"Entering or leaving the EU after 3 June 2021 with cash or certain valuable items worth over EUR 10 000? ... "all travellers entering or leaving EU territory are already obliged to complete a cash declaration when carrying EUR 10 000 or more"
https://taxation-customs.ec.europa.eu/customs-4/prohibitions...
I was traveling recently and when trying to pay for a hotel room the transaction was declined. I needed to call my bank to explain that I am traveling, so they tuned down their anti-fraud alerts. Thankfully, one phone call was all it took to resolve this.
However, this block was only triggered because the transaction in question was relatively high amount ($1500), the very same card would still work perfectly for small transactions.