Make the weekly shop a learning experience with your child. Involve them in the process and help them develop their writing skills early.
When you sit down to write your shopping list, provide your child with a note pad and pen and sit together writing your list.
As you write, talk about what you're writing down "we need milk", "I need tomatoes".
Ask your child what they think you need to buy.
Take your shopping lists with you when you go shopping and refer to them as you go round the supermarket. "This says I need to get some milk", "what does your list tell you to get"?
Don't worry if your child's marks and squiggles don't look like words, your child will be able to recall what their marks mean.
Why not allow your child to mimic you by writing your list below and getting them to try and copy on the right.