Another useful tool that isn't needed often, but is handy to get your hands on it, is a focus calibrator. The one I use is called "Lensalign", but again there are others to choose from. I got mine after I bought my first teleconverter.
I generally use a 70 to 200mm F2.8 zoom for pottering about, when birding isn't on my mind -which isn't often. I use a 300mm F2.8 VRI when I feel the urge to photograph birds. For small birds I add a TC17CII, which gives you roughly a 510 mm lens.
As a pure prime, I haven't found the 300mm has any measurable faults at all. However, if any of the three teleconverters available are added to it, the focus point will be moved towards me. It no longer focuses at the right spot.
The lens align tool has a target which you aim at. It allows you to see where the camera is focusing and so study how the depth of field is being used.
An equal amount both in front and behind the target is what you want to see. But as I've said, with a teleconverter in place, I find that most of the focus is in front of the target, which isn't something you want. If you were aiming at a bird's head, a lot of the focus would be on the air in front of its bill.
Nearly all DSLRs have an adjustment you can use to correct this. They have a menu item where you'll find an adjustment scale to move the focus point to the correct place. It's easier than it sounds and the result, after using the tool, is you won't waste a drop of focus.
Once again, it wouldn't be a bad thing to share in your local club. You don't need to use it often.