If your kids are smaller, then you can pull out different objects - most will start with the letter of the week and some will not. Pull out the objects and let them try to find the ones that start with the "letter of the week". For example, if we were to start with A, then you could have a plastic ant, avacado, art set, airplane, apple, apron, ambulance - or whatever other things you find. Set them out and have the kids say the words and try to hear if they hear the 'a' sound. Put them in your shoe box and you have a letter A box that they can play with all week.
If your kids are older, then allow them to find things around the house that start with A. They could add one thing per day and you can see how many things you can put in the box. If they are running out of A objects, then print pictures from the internet!
What's a good book for A week? The Art Lesson by Tommie DePaolo!!
If your child is working on articulation and already knows his/her letters, then focus on his/her past and present artic sounds!!