Basically none. If you are not using their trademarks, logo by itself - which is entirely different than using the physical product as built by Apple or as modified in any way you please to change it with painting, stickers, or a even a hammer. You probably don't even need a license to show the software if that is incidental to the picture. What you can't do is imply that Apple endorses the film or use Apple products in marketing your film.
If you are thorough, you will want to have a look at both Apple's legal trademarks information and consult with whatever lawyer (or paralegal) is helping you with other legal aspects of making a movie that is familiar with the laws in your specific filming/distribution locations.
Here is Apple's main trademark page:
In it, you are not really a reseller or advertising the movie itself with the product and trademarked design and logos, so read that portion but don't take it too seriously for the things that don't make sense. Pay attention to how Apple prefers their product to be depicted in photographs.
Also - there is a tidbit about mailing Apple directly for product placement.
Marketing or advertising requests (which may include promotions/giveaways, sponsorship, product placement, and partnership requests) may be emailed to email@example.com
You might not get free product to use, but you should get a nice package covering their desires and wishes for product placement. Even if you were using Macs in a light that Apple prefers not to see - you might be covered under free speech and artistic expression rights, but I wouldn't expect Apple to spell out that on their pages - so check with your legal team for that if you have concerns.
Good luck filming your project.