I've never used a cup before, but I know for certain, you can't really do that with tampons, because it would be way too dry and eugh, even imagining that is making me shudder. Most women who use tampons know how unpleasant it feels to pull out a dry tampon; I have to be careful near the end of my period not to use a tampon with too high an absorbency if I want to avoid this. I may switch to pads near the end.

Periods can come without warning though. Some people have a super low flow early on, so they might get more warning (if they go pee and there's a lil blood when they wipe), but also sometimes it's heaviest at the start, which is why many women have embarrassing stories of their period taking them off guard and bleeding through their clothing onto a chair or something. Someone might wear pads if they're expecting their period - you can get lighter absorbency pads that might suit this better. Older women might wear pads like this at other times - my mum occasionally pees a little if she sneezes too hard, so she wears lightweight pads at other times of the month.

It's easier if you can predict when your period will be. I've never had a regular cycle, and I thought the whole "my period is 2 days late and I'm anxious that this might mean I'm pregnant" thing only happened in movies until a friend anxiously messaged me about it. Turns out some people do have that level of regularity - I might actually ask my super regular friend what she does when expecting her period, come to think of it. But yeah, for many people, it can't even be predicted to the day, or even the week.

Edit: reading other responses to your question made me think of amother point: even if you have irregular cycles, it can be possible to predict by various bodily signs. Something that I don't hear talked about much is how vaginal discharge changes over the menstrual cycle. When I'm ovulating, there tends to be more discharge, and it's slippery and clear, almost like egg whites in texture. At other times in my cycle, it might be more white coloured, or more creamy, or more sticky. I find it gross and fascinating in equal measure — sometimes I'll just stick a finger up there to check if I'm unsure where I am in my cycle