Hello,
for personal experience, the first exercises someone should try are very simple: turning on leds and read buttons/switches is quite a good one.
Even more complex experiments may have a LED as a target: I am thinking at a PLL reconfiguration that makes a LED blink faster or slower. I know that the ALTPLL_RECONFIG megafunction does a lot of this job but you can build your own finite state machine to trigger and control ALTPLL_RECONFIG. Then you can do some practice on SDC constraints and PLLs. Just to tell the first non-trivial example that jumped in my mind.
I also remember that while I was a student I did not have so much spare time during lessons or exams so having the board in time for the break should be quite good.
These are my parameters: the choice is up to you.
Regards,
Gabriele