As you are training your dog, start collecting objects for him to retrieve and store them in a bin or box. Put all of these objects out of reach between training sessions, including the slippers, shoes as your dog may carry them off and chew on them once he starts interacting with them. Once the retrieve behavior is under stimulus control he should ignore them unless otherwise directed. There is also a minimum maturity level for him to ignore the objects as well. Dogs that are teething (upto 18 months age or more for some breeds) need to have access to all training objects closely monitored.
Use a variety of objects, all of which are replaceable and non-toxic. Different textures, weights, sizes, materials, larger items to small items, delicate items and hard objects that might be uncomfortable to hold, common objects he is likely to retrieve and not so common. Go through your junk drawer to see what might be safe and suitable.
Here is a list of possible objects:
Dog leash (use harness, vest once trained)
Child’s plastic toy (no small pieces)
An old shoe, slipper or glove
Old purse or bum pack
Old T-shirt (or piece of one)
Empty aluminum pop can
Empty plastic drink bottle with lid
Empty tin can with edges taped for safety
Heavy cardboard roll
Metal spoon, fork, butter knife
Old TV remote control
Rubber or plastic lid
Old glass case
Empty pill bottle
Empty CD case
Small cardboard box
Toilet paper roll
Crumpled paper towel and tissue
Short chain of paperclips
Coins of varying sizes
Fake credit cards or expired cards mailed to you (add a thick elastic makes them easier to pick up at first)
Playing card or business card
To add weight, start with an empty water bottle with a lid. Add an ounce of water each successive training session to find out what weight is comfortable for your dog to carry. When full, you can switch to to a full pop can or soup can. Make sure you practice with the empty one first!
For very small items, start training by placing it on a rug or the dog bed so it is easier to get under, then progress to other surfaces, each a little more difficult than the last.
For example: it is much easier to pick up a coin off a dog bed than it is a slippery laminate floor. Laying down a computer mouse pad or placing the coin on the edge of a smooth table might be intermediate steps. Do what you can with what materials you have to help your dog be successful at each step! Don't forget to ask friends and relatives for stuff they might have that could be useful in training. Check out second hand stores and garage sales for useful training objects as well.
For more advanced training: smear a little spreadable food on items to increase the challenge of bringing it back without licking
Always practice with things that are safe for his current level of training. One day I was taking some money out of my wallet and accidentally dropped a dime. We were training on quarters at that time and my dog surprised me by being able not only to bring it back to me, but to pick it up off the smooth floor. Better to be safe than sorry!