Got a muffin tin? How about some old socks? Maybe some plastic cups..
You don't have to buy all your dog toys, household objects can be very entertaining.
A muffin tin and some old tennis balls makes a great game. Put a treat or two or three in some of the tins, put a tennis ball in all the cups- your pup will find the treats.
Got old socks? tie them in knots and in knots together for tug toys!
Got a few big solo cups? play "3 card monte". Treat goes under one cup, move them around and your dog has to find the treat under the cup.