In relation to “necessary cookies” where (necessarily) there is no need for an opt out:
“We’ve put some small files called cookies on your device to make our site work.”
In relation to analytics cookies where an opt out is required by law:
“We’d also like to use analytics cookies. These send information about how my site is used to a service called Google Analytics. We use this information to improve my site.
Let us know if this is OK. We’ll use a cookie to save your choice.