Can Lid

The cheap moulded plastic food can closures are made to such tight cost limits they inevitably fracture and tear apart especially if put in the fridge a lot, and washed in very hot water. Friends with a small dog that only needed a 1/2-can of food at a meal went through a few and asked if I could come up with a better one that could take a lot of use. This design is as basic as it gets & was my 1st tinkercad effort, but it does the job pretty well.

The stl is of the original which I printed in PLA (all I had to hand). So it had to be a little bit loose to snap over the metal roll-over rim on the can without breaking. Still worked fine though and if it rattling around is a bother, you can paint the inside with some epoxy or latex adhesive. That isn't OK for long-term food storage, but a day or two wouldn't present any appreciable risk of contamination. Of course, don't put PLA ones in the dishwasher! Unless you like modern art! Apparently my friend forgot PLA's glass temp of 55°C is lower than the 70°C dishwasher... So the next batch were done with my nice new roll of Rigid.Ink orange PETG.

To print in PETG (as my more recent ones have been) there are a couple of mods to make in the slicer. First, scale down to 99% - as PETG is a bit springy a tighter fit works fine. I tried one at 98% and it worked but took a lot of effort to press onto the can. Second, use a higher temp than usual - detail is less important than a smooth upper surface (the lower/inside surface when in use) - I go from my regular 230°C to 235. Finally set to give at least 0.4mm thick top and bottom layers. Infill is barely used so anything over 20% will work just fine unless you really care about a glass-smooth surface only your half-used tin of dogfood will ever see.
I'd always recommend PETG for this just because you can get that tighter fit without it exploding to pieces. Plus, in translucent orange, they're the best looking half-used-dog-food-tin covers around! :)