Yes, always know that you don't NEED any particular tool in order to teach your child. There are many tools available, and each has its merits over the other.
The single most important thing is put in the time and effort to teach, and to introduce your child to the joys of learning. So long as you are spending these precious bonding moments with your child and your child is enjoying it, you're doing wonderfully already!!
Home made flashcards are great cos they are as personal as they get! You could even keep them as keepsakes and show your son when he's grown up!