Do you have to have them with every kit?
No. I've been scrapping for a long time and have a million alphas so it wouldn't be essential. Also, I'm a pocket scrapper these days and rarely use alphas. That said, I would probably want to pay less for a kit without.
Do you use them on every page?
Nope. Often just use fonts
Do you have ones that you use over and over?
I don't have ones that I specifically look to but when reviewing all my alphas, I probably do use the same ones more than others. I usually use simpler, bolder alphas. Mostly white.
Let me know your thoughts about the questions above and anything else you want to share.
I know there is a lot of debate about this but I prefer my alphas on one sheet for reducing the amount of storage they take up.
ETA: just out of interest, I went back to see the relative storage space for individual alphas vs a combined alpha sheet and, to my surprise, discovered that they are virtually the same. The individual alphas add up to roughly the same (and sometimes even less) than the sheet. So, never mind that last point.