If the following sounds like heresy, my apologies in advance.
But what if at some point in the future, you want to open a file that you created on your Amiga in its heyday... and your boring modern computer says "huh?"
To avoid that situation, I decided to go over all my old Amiga data from the 1990s (and even early 2000s it turns out even though I got my first PC at the turn of the millennium). Here are some experiences that may benefit others.
The idea was to convert to formats that are widely supported today, and if at all possible, convert to something that allows further conversion to something else without complexity or loss of quality. So for images, PNG is better than JPG. Both are widely supported, but JPG is lossy and PNG is lossless.
Identifying files
On a Mac or other Unix-like system, the file tool is really useful for identifying file types, especially for ones that don't have an extension and will thus not be recognized automatically by modern OSes. For file types that didn't need conversion I generally made a copy with the appropriate extension, in all cases leaving the originals alone.
Images
Most Amiga images are in IFF ILBM, and most of those can be converted to PNG without losing any data. I think the main issue is color cycling. Perhaps revisit IFF images with color cycling and convert them to GIF or something else that animates.
I used PNGTool for this, which will take any image for which you have a datatype. I did end up with some broken images, I have to further check if there is something wrong with the originals or if PNGTool didn't work properly.
Faxes
I used my Amiga to send and receive faxes for many years, so I had a bunch of those to covert. With the right FAXX datatype off of Aminet that should have worked, but in practice PNGTool wasn't able to convert many of them, and opening them in Multiview was problematic due to the large size and only 2 MB chip RAM. But fortunately I still had GPFax installed from way back in 1993 and it opened and printed all the faxes just fine. Later I switched to TrapFax and that also still worked just fine. Not sure if I'd be able to install either of them from scratch today, though.
Samples
Most Amiga audio sample files are in IFF 8SVX. I used Sox to convert those to WAV ( -t wav ). Sox (also available for the Amiga) recognizes the 8SVX files and the sampling rate automatically, so that makes conversion nice and easy.
I got an ISDN card for my 3000 in 1995, and for four years that card served as my answering machine. (ISDN = digital phoneline a few years before we had broadband.) My messages were recorded in native "A-law" format (would be "mu-law" in the US) and that's a raw format, so I had to tell Sox " -t la " (not " -t al ") to make that work. Pretty crazy but fun to listen back to messages from 25 years ago!
Office-type documents and printing
The nice thing about the file types above is that they all convert to something that does pretty much the same thing today. For office-type apps such as word processing and spreadsheets that's much more difficult. Basically you can go through one or more conversion steps to get those document to load in modern counterparts, but you lose a lot of formatting that way, but you can still edit the documents. Or "print" the documents and retain most of the formatting, but not the ability to edit.
Unless it was very clear that one solution was the appropriate one, I generally just did both.
I initially tried to "print" to a PostScript file and then tried to convert that to PDF on my Mac, but that pretty much never worked. A better solution was printing using a Laserjet printer driver and capture the output using the CMD tool, and then use the rather obscure PCL to PDF tool convert those files to PDF for posterity. Resolution isn't great and no color, but pretty decent and not unduly large PDFs. Perhaps color will work with a more advanced PCL printer driver but I didn't bother looking for those.
Wordworth and ProCalc
These would be the office type applications mentioned above. I have Wordworth 6 on my Amiga in good working order. Main issue was the extremely slow printing to PCL. I also converted lots of files to RTF, which is technically a proprietary Microsoft format but in practice lots of stuff can read it, and you at least get the very basic formatting across.
Wordworth also does WordPerfect files, so I was able to use it to convert a bunch of those that I still had, mostly from college.
A big problem was all the different fonts. Files made to be printed on one printer would switch to substitute fonts when changing printer drivers, and usually not ones even closely related. And although RTF conserves font names, in practice fonts were replaced by something pretty random there, too. I guess you can go into the RTF file and manually change font names...
With ProCalc, no easy RTF option, but only Lotus 1-2-3, which was already pretty old back in the day, and I don't think anything I have on the Mac or Windows can read those, but with some effort that should be doable. Interestingly, ProCalc prints in text mode in portrait, so that's nice and fast and mostly just text that you can recover. Or in graphics mode in landscape, which is much slower and you get to see the Amiga's bitmap fonts in supersize pixelated glory.
Text files
Of course we've had plain text files since the dawn of computing, and I bet we'll have them to the dusk of computing, too. If you're on a Mac or Linux or something like that, plain ASCII files made on the Amiga will work just fine. (That .txt extension does make things easier, though.)
On Windows, you may want to convert the line endings.
But mostly, you'll want to check if those files have any "high ASCII" characters in them. For instance, in your book reports on the Brontë sisters. The Amiga used the ISO-8859-1 encoding for those characters, while we now use Unicode, mostly in the form of UTF-8. So I made a little script on my Mac that uses the iconv tool to create a copy with UTF-8 encoding and the .txt extension.
But check with file first, if it says that a file is ASCII, it doesn't have any offending characters and no conversion is necessary.