"more activities" is correct and usable in written English.
You can use it when referring to multiple activities or events. For example: "The summer camp offered more activities than last year for the kids to enjoy."
The more activities, the lower the risk.
"We're doing more activities than during regular school".
During the day, there were more activities than any one person could handle.
Once the touring and hiking are done, there are more activities for children.
Reservoir Range also plans to add more activities, including fishing, rowing and other kinds of shooting.
"That's good for safety, but there's room for more activities that enhance their lives".
She told the Financial Times: "ITV has to look at exploiting more activities beyond spot advertising.
There are a lot more activities available to tourists than there used to be.
"There are more activities for youth on the other end of town," she said.
It might simply be that the young person needs more activities and engagement.
If I could, I'd add even more activities; I'd like to try paragliding.
