No matter where you will host your casual wedding ceremony and decide to send out your casual invitations, do you think the rule in wording is beside the point? You still need set stand wording. Be sure that you get all the pertinent information and much better to insert some creativity of personality. However, the whole point of your wording is—casual. Beach weddings are usually, by their nature, casual.
Certainly, the minimum information you must have on invitation cards are the names of the couple, the date and time, and the location of the ceremony. Maps or directions should be included on a separate page, and an RSVP date should be indicated. It can be as simple as saying Name and Name invite you to their wedding. You can be more effusive as you like, but simple will always get the point across.
You may demand invitations play to the casual wedding theme or style. One thing to be mindful of is writing something simply enough that all the invitees will understand. If you are going to use wording for a casual wedding invitation that alludes to how you met in some oblique way, again, keep it simple.
Many themed weddings will involve costume, which is casual only in that it is non-traditional. If yours is one of these, your invitation must include pertinent information. Guests will need to know what sort of dress is acceptable and where to get it. Where possible, you should note that some things can be provided.
Even for a casual wedding, you can still set up a wedding website or blog to give further information and answer questions easily. In fact, if you want a really casual invite that is eco-conscious, you can use an online invitation service instead of sending out paper cards.
There are no hard and fast rules when it comes to wording for casual wedding invitations. Simple and direct will be a great first etiquette step towards a lovely day. As long as you cover the basics and create an invitation that matches your wedding, you can get the word out to every guest easily.