Yes, as Alfie says, a lap of the course is a must. perhaps stopping off at various iconic landmarks? Glen Helen, Sulby crossroads/straight, Ramsey Parliament Square/hairpin, Bungalow, Creg, the list can go on and on! Wherever you recognize from the TV/radio/films!  The heritage railways finish operating on 5th November, so you may be too late for those. Peel is good, as has been said, specially for the sunsets. Down to The Sound for a brew & piece of cake (presuming the cafe is open!??)  The scoreboard/grandstand is a good shout, that's very iconic.  Castletown, for the castle & harbour springs to mind. I'm sure there will be other really good suggestions,but I've got to go to work now!!!
Have a good trip, try & make it for the TT, you'll not be sorry!