Congrats on your April baby! I had one last April. With DD I didn't leave anything beyond two weeks plans b/c she surprised me FOUR weeks early.
This time I started prepping earlier just in case he came even earlier.
I left a Curriculum guide as far as things that needed to be covered in the remainder of the year. I also left notes on various things: rewards/consequences, homework policy, behavior chart system, schedules to everything, where to find things in the room (TE's, art supplies, math manipulatives, etc...).
I started typing this about a month before I delivered. Any time I thought of something else, I opened the document and added to it.
I didn't expect her to follow everything like I do, but I wanted her to have a jumping off point to go from. My Sub LOVED it! She said it was the best thing ever.
I put it all in a binder and left it where she could see it. I also left two weeks worth of plans.
OBTW, the little turkey DIDN'T come earlier than his sister. I just knew he would be here at 35 weeks, but they sent me home with no baby. I was dying! I had never been pregnant so long. He came at 37 weeks though so I got three extra weeks with him.
Best of luck!