Nicholas Hammond - the original Spider-Man, especially how the event banner photo features Spider-Man on it :)
Nicholas was also in The Sound of Music and more recently, Once Upon a Time in Hollywood
Christopher Plummer (Captain Von Trapp from The Sound of Music) please! And especially while there is still the chance to meet him!
Daniel Truhitte (Rolfe from The Sound of Music)
40th Anniversary of The Amazing Spider-Man (1977), the first live-action TV series - Nicholas Hammond as Peter Parker.
Nicholas Hammond also starred as Friedrich von Trapp in The Sound of Music, which recently had its 50th anniversary
Nicholas Hammond (Spider-Man 40th Anniversary & The Sound of Music)
Also would be great to see the Harry Potter stars together:
Daniel Radcliffe
Emma Watson
Rupert Grint