The thing about keeping things ticking over in the holidays is that for KS1 this is easy enough to do and a lot less boring than working through a book of worksheets.
reading: books, recipes, cartoon speech bubbles, poems, instructions
writing :stories, thank you letters, shopping lists
maths, counting in twos, fives, tens (combine this with counting money, working out which coins you could use to buy something like an apple which costs 25p or a book which costs 90p).
counting on over tens / hundreds( start at 25, count on in tens)
counting back in this fives tens
Look for shapes , learn their names, compare their properties, use the vocabulary, straight , edge, curve, curved, angle,triangle, rectangle, circle semi circle, square,
weigh / measure dry and wet ingredients for cooking
learn the o clock times. Learn to set a time
yes these all require some input from you, but have the advantage that your child is learning that maths relates to real life, and, if you ask him to talk about what he is doing he is embedding that learning verbally, and developing the skill of explaining his thinking, which is something schools are really beginning to focus on.