I am making a poster (24 x 36) with multiple jpg photos (44 photos all different sizes) that I have sized using clipping masks. When I'm done and ready to export (both to pdf and jpg - either will work in the end), the file is too large to upload to the printing company. How can I either reduce the final size of the file (jpg or pdf)? I've tried flattening, but I don't think that's the issue.
I have read several posts on deleting excess content outside the mask, but they are all talking about vector items rather than photos. I'm wondering if there's a better way than the eraser tool.
Much of what you wrote is not logical usage of Adobe products, but fear not you have come to the right place. jpg is an rgb digital format, printing in CMYK 99.5% of the time unless your printer is doing a backlit Lambda.
You should talk with your printer about this to ensure your poster prints correctly. I can estimate that at 24x36" you could save a PDF at 200dpi with high quality on the compression for your pdf, which would give you a smaller file size and not sacrifice minimal quality that would be hard to notice.
If your project is all photos, you could have done this in Photoshop, which would be easier/faster
The eraser tool will not work on photos in Illustrator.
Try opening your .ai file (with pdf compatible turned on) in photoshop to bitmap and save your pdf from there.