Although I wouldn't recommend reading it at your desk if you work somewhere terribly serious where laughing out loud is not de rigueur ... laughing is wonderfully good for you so it would be a shame to suppress it!
The letter is basically a very amusing rant about how unappetizing and unidentifiable the food looked. There is a serious point to this, and that is that presentation plays an important part in food selection. This makes sense - if something looks unappetizing you assume it won't taste nice and avoid it and if something looks delicious you can literally start salivating before you've even tried it.
This is why it's important to spend a bit of effort on presentation when you prepare food yourself, particularly if you're preparing a healthy meal when you'd really rather be eating pie and mash! Serving food on nice crockery and taking care over layering/placing the ingredients on the plate can make all the difference.
Using ingredients with a variety of different colours is also important. Ms Haribo, for example, has a very strong aversion to eating foods that are all the same colour (nobody ever serve her fish in white sauce with cauliflower) but actually this aversion is a very healthy one - different colours in foods signifiy the presence of different nutrients so eating a colourful diet is much better for you than eating a monochrome one.
And of course there's another lesson in this, albeit an obvious one - always pack some snacks with you when you fly long haul!