I would think that any flower in yellow, orange or red would look great together. For sure you can do drop flowers in thos colours! Yellow lilies. sunflowers, gerbera daisies, even regular daisies. I got married in September and i had orange/yellow roses that were tipped with red...gorgeous! In the bouquet was also baby's breath and little tiny miniature daisies. You could easily do the 2-tone roses by using 2 colours of icing or by striping your bag.
Check this out....I just did a Google Image Search for "fall flowers"...it brought up some very pretty arrangements. Maybe just pick 2 or 3 from what you see here and go with it. I even saw a few with dark, deep red roses, as well as orange roses.