I also like doing lots of itty bitty (short) bouquets, as sightlines are very important to me. I buy 1-2 "big" bouquets (Trader Joe's often has stuff that's good to mess with) and then divide them up amongst my many-many little vases. Goodwill is a great little-vase resource, Pier 1 is good for new ones.
Like osso, I also just go out in the yard and get this and that -- snippets of pretty leaves, whatever is alive and interesting.
Agreed that linens are a great way to add color/ interest. (Tablecloths, runners, napkins, placemats...)
Can also make napkin rings -- wire, some glass beads, whatever strikes your fancy.