Here's a quick missing beginning sounds practice set for the following letters:
b c n p m r s t
Some of my kindergarten students are still struggling with identifying the correct beginning/initial sound of a word and labeling it with the matching letter. This could be used whole class or in small groups. If used in small groups, I would actually give each student a set of the targeted letters to touch and use to place on each picture PRIOR to having them record the letter.
Encourage your students to get their mouth ready a la Guided Reading prompting.