Craft stores can be your best friend. In the wood section you will find all kinds of usuable objects. I got buckets, barrels, square blocks, rectangles, rounds ect... A little imagination can go along way for cheap money. Glue a square on to a rectangle piece and you get a table. Upside down buckets are now stools.
The whole store is a gold mine though. The plastic pillars from the cake section are great. They have 1" bases and come in different sizes. The doll house section had "leather" bound books, candle sticks, plates, bowls serving platters. A plate or serving platter could be used as the magic shield in the treasure pile. Rhinestones and glitter make good treasure piles. Just take one of the flat 1" square tiles of wood and add gold glitter and a few rhinestones. Mix a little white glue with water and pour it over the mess. It dries clear and now you have a treasure hoard. You can get different colored moss from the floral department and use it as any outdoor terrain. And when done just shove it back in the bag. bags of pebbles are good for a lot of things. You can use the white glue and water trick here too and come up with your own dungeon tiles. Add a pinch of the moss between the rocks to really add some great detail real easy.
And sculpy is great stuff. Really easy to work with, dries quickly and is easy to paint. It can be used for anything you think deserves a little added detail.
Its also fun to burn some of the wooden pieces and keep those "damaged" pieces handy. Really great to use with the players who think the best strategy is to throw a fireball in the room and pick off whatever is left. Once you replace all the items in the room with burnt pieces, it really makes them wonder what they just ruined.
I can go on all day like this....
Gregg