No matter how many expensive "store bought" toys I buy for my dog (and she has LOADS of toys), she still loves the things that were headed for the garbage or the recycle bin.One person's refuse, is another person's toy

In particular she adores empty plastic two liter soda bottles.After ripping off the label she loves to lug these around, bat them with her paw, and chase them. They are lightweight, very durable and dogs seem to like the fact that they can make banging sounds when they hit them against a hard floor.Previous dogs of mine have also loved this "toy".
Another favorite of my dog is the large plastic containers that Marshmallow fluff (or Ricotta cheese) comes in. She also likes to toss these, chase after them, and burrow her face in the container.These are also amazingly strong.
So, if you have a dog, consider whether you should hang onto the soda bottles, or the cheese containers, to amuse your little darling on a rainy day.As long as the material can't splinter or be ingested it's probably safe.