I never carry cash so whenever a beggar asks, I say as much. One guy I encountered recently, jokingly said "I take credit cards too!" If he actually did, he would probably clean up.
I believe it is more about cash being more physical and thereby more immediately noticeable to the perfomer who can give the donator acknowledgement that is the major issue, not the technical transfer aspect.
I guess next step is to have performers carry a small LCD screen and an Arduino to instantly acknowledge received transfers to make it more "physical". (Wooah..! YC, here I come! (jk)).
[1] https://sv.wikipedia.org/wiki/Swish_(mobilapplikation) (Swedish)
If you use ATMs with any frequency, you need to get a free checking account and debit card with a bank* that will refund your ATM fees each month. Once you have one, the higher the ATM fee, the better you feel.
(*I use Schwab, particularly because it refunds ATM fees internationally. In general, just about any online bank -- e.g., Ally -- will also refund fees at least domestically. Many credit unions probably do this as well.)
(source: several friends who busked a lot)
Also, there are a lot of places in NYC where they still take cash only, especially bodegas and dive bars.