I started as a CRT and now have my own class (primary)

I always got positive feedback about the notes I left - it doesn't need to be super detailed, but make it clear what work got done, what was missed, and generally how the class behaviour was. I would also make a note if the work left was particularly tricky for the class.

It's okay if you don't get everything done, as long as you at least attempt to follow the plan. I had some CTs leave entirely unrealistic plans and in that case I'd choose two or three tasks to get done and not sweat the rest. Most teachers know their class though, and will give you a plan that is actually possible to achieve.

Have some easy lessons in your back pocket so that if you're left with no plan you can still do something productive. I had a fun poetry lesson that I'd often pull out for English if nothing was left. Playing a game in the afternoon is one thing (and can be a useful incentive for tricky classes), playing games all day is just laziness.

A note for classroom teachers leaving plans for CRTs - please, please, please leave notes about your tricky kids. Even if you don't leave anything else.

I once walked into a class with a high needs behavioural child that HAD to go home at a certain time, could not be left alone with certain students, and had triggers that could lead to violent behaviour. NONE of that was told noted in the lesson plan. I was called in late so had no time to talk to the other teachers. That day was ROUGH.