My best sub £20 accessory was this pod...
... which cost me £9.99. It screws into the tripod mount of camera or lens and is ideal for resting on car or hide window frames, walls, fence posts, the ground - anything really. I've even taken to carrying my tripod around and just plonking the camera with pod attached on top of the mounting plate. This gives lots of stability but also a fair degree of movement for framing the subject and if you suddenly want to track a bird in flight it's instant.
Dave P.