Both my failures were on C-152's.
The first, during my private, the transmitter on our comm radio died just before entering our class D airport. We decided to divert to an uncontrolled field, land and call the tower on a cell phone to let them know our intentions. The funny part was that they made us squak 7600 but the transponder decided to report 7700 instead. The tower switched us back to 1200 immediately.
The second was a vacuum failure just about 10 nm from our base airport. We were VMC so it was not a big deal, the good learning experience I've got was to actually see what happens to the instruments. The first thing I noticed was the DG card spinning rather fast, there was no immediate indication of a failure on the AI during level flight, the vacuum indicator needle was all the way down.