The best way to make your car less tempting to would-be thieves is to avoid storing your valuables in it. If you absolutely have to, though, this little DIY trick will help you hide them in plain sight.
Whether you have no other place to put your valuables, or you need a place to hide your auto essentials like car repair tools or a first aid kit, this trick should help keep them from getting stolen. Just put your belongings in a cardboard box, and staple together a false top — filled scrap cardboard and other trash — and just cover up your belongings with it. Of course, this doesn't guarantee your car will be safe, and we'd still recommend keeping valuables on your person whenever possible, but this should help keep your car among the less attractive ones on the street. Hit the link to read more.
Disguise Your Stuff to Prevent Car Break-ins [Wise Bread]