This is a broad question so we're going to tackle it from a couple angles.
The number of repeat callers
If you have a lot of repeat callers that are on hold every time they call, you're probably going to want a relatively long on-hold audio production with several messages. These messages should have information about your company, how callers can reach you besides the phone (think email, fax, and social media), any current specials or promotions, answers to any questions callers frequently have, and any information you'll need from the caller when a representative returns to assist them (order numbers, account numbers). A long production means it's likely that the caller will hear different information every time they call, and they won't be irritated by repeating messages if they're on hold for a while.
If you have mostly first-time callers that are not holding as long, a shorter production would work perfectly. You can include the same type of company and contact information, answer any frequently asked questions, and share current specials and promotions, but it's imperative that you keep the messages very short and focused so the callers will get as much out of them as possible.
Many businesses offer seasonal promotions. If you have special sales, rates, or season-specific inventory, that's a great starting point for your message on hold. If your company sponsors or participates in charitable events or seasonal festivals, let callers know where they can meet you in person. Your office may be closed or open special hours for specific holidays or during certain seasons, and this type of information is important to callers.
Another way to add a seasonal slant to your on-hold audio is with music. During the holidays, use festive (but non-denominational) music to your production. Summertime is perfect for a Latin or Caribbean beat, for a fun beachy feel.
You could also use seasonal wordplay to liven up the messages, share weather or health tips, home or vehicle maintenance ideas, or even simple recipes or meal suggestions that feature seasonal ingredients.
Your update schedule
A major factor in the decision of what to include in your on-hold audio is how often you will be changing the production. Unlimited programs are the most flexible, allowing for the addition of time-sensitive events...just be sure to schedule updates to remove them as they pass. Will you be making changes every month? Include information about your monthly specials or sales. Many seasonal businesses choose a quarterly program to advertise different products and services as the seasons change. With a semi-annual or annual update program, you want to make sure you are not mentioning anything time/season specific, and keep it more generic.
For more ideas, including our suggested best practices, check out this link!