Best way to keep track of which pill comes next without hinges?

I've done a few one-piece organizers with sliding covers and the trick is to design the whole thing as print-in-place with the slider channel printed as a bridge, not an overhang. If the roof of the channel is flat and spans a short gap between two walls, the printer just bridges across it and you get a clean enclosed slot with no supports at all. Keep that gap under about 20mm and it'll look fine even on a basic machine.

For the roll-top motion, model the cover like a curved strip, think of the shape of a tape measure or the slats on a roll-top desk. It sits in a curved slot cut into the top of the body, and as it slides it curls back on itself. The slot's inner surface is what you print as bridges. I left roughly 0.4mm clearance on each side of the sliding surfaces and it moved smoothly after one pass of working it back and forth. Do a small test piece first, just a 30mm section of the channel and cover, and print it to dial in the clearance for your machine before committing to the full print. On the overhang question, you're right that past 45 degrees things fall apart, but you don't need steeper walls. Use chamfers instead of curved fillets on anything that slopes. A 45 degree chamfer prints perfectly with no support, so any transition where a wall meets a floor or a channel edge, break it into a 45 degree step. Curves are the enemy, chamfers are your friend. Same for the little guides inside the channels, put a 45 degree chamfer on the bottom edge so the first layer of the guide doesn't hang in mid air. One more thing, orient the print so the sliding direction runs along the Y axis and the channel roofs bridge left to right. If you rotate it wrong the layer lines act like brakes on the slider. With the cover captive in its slot it can slide partway open, the open day is obvious, and it physically cannot come off the body. No hinges, no glue, no screws, no supports, and it comes off the bed in one piece.

One thing that helped me with print-in-place sliders was printing a tiny test block first, like a two-inch section of the slot with the cover piece inside. My clearances were way off on the first try and I would've wasted a whole day of printing. Also don't forget a brim can mess up sliding parts if it fuses to the moving piece, so check that before you walk away.

Reminds me of the old vacuum forming days, we used to do the same trick with wooden test blocks before committing to a full run. Anyway, one thing I'd add from my own pill organizer attempts: don't let the printer cool all the way before you work the slider loose the first time. I cracked a cover once yanking it off the bed cold, the moving piece had welded itself down with a few too many first-layer squish lines. A raft-free first layer and a slightly raised z offset on the body only helped mine pop free intact. Also, if your slicer has the option, turn off ironing anywhere near the channel, it swells the top surface just enough to bind a tight slider.

I'd push back on the 20mm bridge gap advice. On my old bed slinger anything over about 10mm on an enclosed slot like that sagged in the middle, and the cover jammed right at the sag point. If your machine has decent cooling you might get away with it, but on a basic one I'd break the channel roof into two shorter spans with a little middle rib instead, the rib just becomes a ridge the cover rides over. Also chamfers on the inner guides are fine but they eat into the sliding surface if you're not careful, I rounded one too much once and the cover had side to side wobble the whole length of the slot.

I went thru the same thing building a day-by-day med caddy for my dad last winter. What saved me was switching to PETG for the slider parts, PLA had so much friction between the layers it felt like sand. PETG slides almost greasy once you work it in a few times. I also printed the whole thing standing on its back edge so the slots faced up, which kept the bridge spans short across the narrow direction instead of down the length of the body. One thing I never figured out was stopping the curved cover from wobbling side to side in its slot, did anyone find a way to keep it tracked straight?

Quick update — I went and printed a two-inch test block like one person suggested. My initial clearances were definatly too tight on the slider mechanism. It was a small adjustment, but printing the section proved the bridge design works when the tolerances are right.