That would depend on your knowledge of the basic principles of the toilet and whether or not you use one as part of your daily hygiene.
The toilet can be useful to someone else, but not to you, it's simply a matter of perspective. I rather suspect you can answer this question yourself. Now if you've never used a toilet before and are inquiring about them, of course, they are very useful.
Toilet paper, condoms and mars bars.
There is a few inventions that are not very useful. The most known invention that is not useful is the toilet paper roller.
life is like toilet paper....Long and Useful
Exceedingly. Other than that you would just use leaves or your hands!!
You have probably got your period or you might have a UTI (urinary tract infection) I hope you find this useful!
it creates vitamin D which is healthy for your bones.
cheese
All reading materials are appropriate, except for study material and difficult books. It might be hard to make useful notes while on the toilet. Magazines are the best choice. The time it takes to read one article will usually not exceed the appropriate time for using of the toilet.
The availability of online coupons for toilet paper depends on what country you are from. I find it best to email companies and ask them if they are willing to send me out some coupons. You usually end up with coupons that are worth more money this way.
Some say that the merchant in your toilet is Mary Jane. Unfortunately, Mary Jane does not exist. The merchant in your toilet sells fudge (occassionally melted) and lemonade. Why? We do not know. What kind combination is lemonade and fudge? A horrible one. Also, every time you try to pay him, you put it on the silver handle thing that is his hand. Right? Then, he sucks all the merchandise (and your money) into the toilet. How annoying! I hope you find this information useful.
Maybe tissue box or toilet roll? You can use it to make into a robot or something. It could be decorative.
Yes, you can adjust the toilet clog to clause your toilet to overflow.