There are lots of great and unique options for window coverings. "EH" cannot put holes in window frames to hang new curtain rod that could hold light blocking curtains since the place is rented. I can assure you "EH" there are other options than brown grocery bags!
Idea #1: Get tension rods (two for each window top and bottom), a heavier fabric that will keep light out, and some fabric glue (in case you do not want to sew). Cut the fabric a few inches bigger than window opening so you can fold fabric over to "hem" on each wide. Make a "pocket" at top and bottom for tension rod. You can glue the fabric right over the tension rods. Hang and voila! Light blocking, but not as sketchy as grocery bags! Could look a little something like this!
Photos from Apartment Therapy
Idea #2: Get a heavy fabric and measure full length of window, hem as suggested above using fabric glue. Finally, add ribbon "tabs" at top and buttons. You can tack to top of window with small tacks (landlord will never notice few tiny holes)! Or, if fabric is not too heavy, you could use heavy duty velcro that you can pull of when you move. Paper bags.... what?
Photos from Sunset Magazine
Idea #3: Just cannot give up idea of paper? Cut paper size of window (or two to fit). Get a pretty paper, not grocery bags. You could glue ribbon trim around paper to pretty it up a bit. Use tacks or velcro to secure paper to window frame and you have yourself some lovely light blocking "window treatments", kind of like what is below!
Photos from Drake House Museum
If you just need privacy, not light blocking, you could use a transparent paper or vellum! Something like this (see below). This a film that sells for $76, but could be easily recreated with paper from an art store.
Photos from 2Jane
Now yes, all these options do require a small amount of crafty-ness, but "EH".... you can do it! Keep me posted!
Until next time....xoxo