If I'm being honest here, I think it's a complete crapshoot. The Cart guys at our store have just worked in that category (along with cashiering, obviously). But it never hurts to go up to your STL and ask him/her if you can be cross-trained in, let's say, Presentation and that you would like to split half your time on that side. Most TLs would appreciate that you're trying to learn new things, so I would definitely go that route and ask about cross-training.
However, there are anomalies. We had an ETL at our store that started off as a cart attendant when he was a teenager and he eventually worked his way up and now he's currently in training to be an STL. So, it does happen. Just do the best you can and learn as much as you can.