"Soda pop" seems redundant today but that's what I remember calling it when I was a mere New England pre-teen around the middle of last century.
"Soft drink" itself is a bit of a wry joke of a name. The implication is that a real drink is a "hard drink", that is, one that contains alcohol. So, theoretically, one should not call it a "soft drink" unless alcoholic beverages are also being offered in the same setting.
I think in days of yore, soda pop also used to be called a "phosphate". Phosphoric acid being a major ingredient of many cola type soft drinks. Apparently in diners and even drug stores, one could plop down at the counter and ask for a custom made "strawberry phosphate" or some other such flavoring not often found in bottled or canned equivalents today.
Oddly, there isn't much sodium in a modern "soda". I suppose the name comes from the fizzing that a preparation like Alka-Seltzer would do, and Alka-Seltzer did indeed contain sodium as part of the bicarbonate. Just as well - the soda gives it a bitter taste that probably wouldn't be at all to the liking of today's tots.
Speaking of yore, does anybody still have a spritzer bottle? How does it work? Do you attach a little C02 cartridge to carbonate the otherwise ordinary water?