Debbie, I hope I can help you since my parents just celebrated their 50th Anniversary this year.
If you can't get the whole wedding album then try to get a couple of framed photos of their wedding day to display. I also framed a recent photo of my parents together to put on display.
I also went to a party store and got a guest book that said 50th Anniversary on it and had everyone at the party sign it and write brief messages for them to look over later. Also at the party store we got a couple of bunches of gold balloons (for their golden anniversary) and a couple of mylar balloons that said Happy 50th Anniversary on them. After the party I let the grandkids each get a balloon to keep. I also found a banner that said Congratulations on it so I think that the banner idea is great, even better with balloons.
Also take lots of photos or bring a couple of those disposable cameras for people to use.
I would check with the local bakery/grocery store about the cake, they should be able to come up with something sugar-free for a diabetic or maybe do a tray full of sugar-free cookies/brownies or something else instead.

You should also search for Lut's thread about her parent's recent Anniversary, I think she made a nice photo collage as a gift to her parents and she posted photos of it too.
Good luck and have fun!