I use a random map or dungeon generator like gozzys, here , download the ones I like as png files and just drag the file onto the tabletop. Resize and move to the map layer, and then I can add dressing or even entire rooms. I also keep spare maps as png files that I can put onto a page when the PCs decide to go somewhere I haven't prepared. There are other map generators out there of all kinds. I also like to use historical maps from cathedrals or medieval cities or Roman ruins. For furnishings and added textures, the free stuff available by search on the tab is pretty good, as Brian A says. You can make it a little more varied by applying tints, which stay even after the item is turned into a drawing on the map layer. When you click on the token, while it's still on the object layer, the gear-icon at the lower left creates a menu that has the tint option. As long as you are not doing anything for money, you can copy images from any source, but if you are doing anything that could be interpreted as profiting, don't go down that path. If you have image editing software you can do a lot. The special effects available in powerpoint are enough to personalize a lot of images, and you can remove backgrounds, crop, rotate, mirror image, etc. Right click on the image on the powerpoint slide to save as png file. Rolladvantage has a tokenstamp tool, here , that you can use to easily create portrait-type tokens using artwork from anywhere. I use it for characters and NPCs. You might find a way to use it for other furnishings too. Once you get going, you'll find your library growing pretty rapidly.
