I'll add my voice to both of these.
Having just returned from two weeks in the fourth poorest country int he world...
As a US resident with well established access to banking, a smart phone on my person, multiple cards in my wallet, etc., I still use cash. Often it's more convenient to pull out a few coins or bills than to go through some other payment process. And there are the charges applied to the vendor and/or me; when I give my money to a store, I want to pay only what the marked price is and I want it all going to the vendor.
I just wish you guys (the US) would adopt a dollar coin, and maybe also introduce a $2 coin! I come home form a launch day and think "Look at this fist full of dollars!!" and in fact, it is about $13 in ones.. I know you have them ($1 coins) and I know you have (although very rare) a $2 note...
I too often find my wallet full of too many singles. The Treasury and/or Federal Reserve would save money by using dollar coins instead of bills. They've made half hearted attempts before to get the public on board with that, but they won't do it the right way. They issue dollar coins, wait for their acceptance, and say that then they'll stop with the bills. The public never makes the switch because the coins are new and strange. What needs to happen is the issuing of coins and the simultaneous cessation of printing the bills. Let the circulating bills age out naturally and people will easily get used to the coins when they have to. Right now there about a billion of the coins in bags because Congress commanded production numbers for the presidential coin series, so the up front cost of the coins to do this would be greatly reduced.
On the other hand, I wouldn't want the five to 10 singles that are often in my wallet to be suddenly replaced by 40 to 80 grams of coins in my pocket, so a $2 denomination would be necessary. A new $2 coin would require Congressional action, but to increase printing of the $2 note would not; it is allowed under current law.
OK, so, all that is about my current use and future wishes. But what do I think
will happen in ten years? Frankly, not much. I think the cashless society and the change in $1 and $2 denominations are both pipe dreams.