Moving files, best workflow

I am preparing for a big presentation in June. Essentially, I will be preparing a series of slideshows that will play all day throughout the event. I will have three devices that contain the slideshows and there will be a switcher to go and forth between them as necessary.

To build the slideshows, I am working on both my desktop computer and a laptop. I will take the laptop and an iPad with me to the event. All of my photo and video clips are stored on dropbox. How should I set this up for the best possible outcome? Leave the media on Dropbox? If there is spotty internet service, will my slideshows still work? Should I create a local folder with standalone player versions of each slideshow? Should these standalone apps be saved on the laptop hard drive or an external hard drive? Can I put standalone files on the iPad? If I copy all media files from Dropbox to the external hard drive and the file structure is different, will everything break in the slideshow?

I would greatly appreciate your help with all this. I have been given this task, its a big responsibility, and I want to do a good job.

Thank you,