I also try to tip more than once. I don't have time to go through each comic and tip them all the amount that I wish I could, but whenever there is a new episode that I particularly enjoyed, I will tip them again. So the more a creator updates, the more likely they will receive multiple tips from me.
Although, if I have tipped them a fair amount more than other creators that I follow, then I hold back on tipping them for a while so that I can tip other creators first.
I'd love to be able to support creators in other ways, such as buying their merch, but as someone who moves around a lot, I don't really have the space for more things. I'd be afraid to ruin or lose it in the move. My moves aren't exactly small either. I tend to hop around my country (and soon the possibility of other countries), and that's saying a lot since I live in the second largest country in the world.
As for digital copies, call me old fashioned, but I prefer physical copies if I'm ever to own one. There's nothing quite like holding a book (plus new book smells! ^^).
That's what makes the tipping program so enticing to me. It allows me to support these creators without actually having to buy anything. Patreon is always a solid option as well if you want to give more regularly without having to actually think about it all the time!