2-Trying to take a little bottle from floor when you are riding.[This is for balance]
We used to do one like this when mucking around, only we used coins instead of bottles when playing on road bikes. You stand them on edge and see what is the smallest you can pick up- I could get a 20c (~30mm dia, 2.5mm thick) but some others (fnr world jnr kilo champ) could piock up a 5c piece (19mm dia, 1.25mm thick).
Of the others the only one I havn't tried is ridint the rollers with my eyes closed, but I had a set of rollers only 280mm wide (std about 600).
I can do the stopped blaancing 1 handed, and on a good day with no hands.
Instead of a "Z" between the bottles try a "8" around them
I also think wheelie practice is important for MtB as well.
For road and track more than MtB (not that I havnt needed it for MtB) go to a grassy field and try and knock each other of your bikes while trying to stay on yourself.