The Pills Note is a reminder Bill wrote to himself, found on the floor at the far end of the room up the stairs and to the left after you drop through the broken fence in The Woods section of Bill's Town.
Bill reminds himself to gather more pills and ammo, and keeps crossing out how many weeks remain until his next drop-off with Tess, ending on three.
It connects back to Tess's List from the previous chapter, which logged the pills and supplies Bill sends to Boston. It is also one of several notes Bill leaves around Lincoln to keep track of the town.
Bill's Map
Bill's Map is Bill's hand-annotated map of Lincoln, on a table with an engine near the door you come in through at his safehouse, right after you meet him.
Bombs Note
The Bombs Note is on a table to the left in the side room off the nave of Bill's church. Go into the room on the right, the one Bill makes clear is not the confessional.
Boy's Diary
The Boy's Diary is on the windowsill of a child's bedroom painted with stripes and cars, upstairs in the second house with the dry pool in the new territory beyond the church graveyard.
Fences Note
The Fences Note is another of Bill's reminders, on the table in the back room of his safehouse near the pipe he handcuffs Ellie to.