I like to use Amazing Mold Putty to make my own molds with stuff I have, e.g., brooches, lots of other things. I only do small things. I haven't tried to do a whole sheet as is shown in the second link that HamSquad posted.
I wander around the house looking for things that would make a good impression or mold. I also check out the dollar store or thrift store for things to use. I scrub these things thoroughly (and rinse with bleach if possible) and it is extremely unlikely that the small amount of time the object is in the putty it would transfer "toxic" elements or that those would transfer to the fondant used in the mold.
I am in my office right now (and should be working, shame on me) and looking around I see things with interesting patterns--my pencil cup is metal mesh, my water bottle has an interesting "corrugated" design in the plastic, one of my paperweights has an interesting pattern on it, a takeout container from the cafeteria has different kind of corrugated pattern, etc.