I just had an incident two weeks ago where my best barista was opening on a Saturday and got a rush long before I was scheduled and she kept calling for backup. My ETL was there, came up, and told the guests "Sorry, there isn't anyone in the store to help her." Yeah I was pissed, so was my barista. So I told my ETL the same thing I tell anyone who is afraid to ring in Starbucks - you won't know what you're doing, you will feel like you're in the way, but I guarantee you that you will help out far more than you realize. All we need is someone to stand there and talk to the guest and take the payment. We can listen out and help you ring it up and get the right cup. We just need someone to greet the guest, push a couple buttons, and take the payment. It's a huge help.
(Ok end of small rant.) I've cross trained a couple GSAs and a sales floor TM recently to help out with backup. Any ETL should be competent enough to do what I've described above. But this is just for backup, which generally isn't an issue at my store.
As for call offs, that's pretty much me. I've probably covered about 150-200 hours worth of call offs in the last year. I even came in for a half hour one day because there wasn't going to be anyone to cover a break in Starbucks after the ETL-HR screwed with my schedule without asking me (and then I stayed another 15 minutes to cover the food ave break because why not lol). Maybe a dozen 14 hour shifts in the last year for various reasons. I have over 200 hours of vacation+personal time, so I generally just schedule myself for 32 hours and then cover any call offs or actually take some vacation (just kidding I don't end up getting vacation, that's why I have 200 hours). Although the call offs have slowed down ever since one person got put on corrective action.