When was the last time you saw somebody wrestle with a map behind the wheel? Or look up that Spanish word in a print dictionary? In the smartphone age, those kinds of reference materials are available at the touch of your screen.

Post-its, likewise, are no longer used to used to remind us to pick up milk on the way home. After all, you've got your entire shopping list on your iPhone 6.

Some things, though, are so important that they might warrant a special - and, dare we say, non-digital spot. So if there is something you need to remember all the time, every time, why not turn your smartphone into an old-fashioned, analog mnemonic device. These cool cases for the iPhone 6 and iPhone 6 Plus will do just that:

  • Who, on his or her way to work, has not experienced the terrible angst that comes from having forgotten antimony's standard atomic weight? Well, have no fear - thanks to Redbubble's "Mendeleev's Periodic Table of Elements" case for iPhone 6, which will set you back $25, but set you straight when it comes to the lustrous gray metalloid. The nifty little device costs the same for the iPhone 6 Plus and also comes in a "Tough" (as titanium) and a "Skin" (as mercury) one for $15.

  • If chemistry is all Greek to you, but Greek isn't, then you might prefer the "Greek Alphabet" case, also from Redbubble. The prices and the varieties are the same, but this case is sure to remind you of just what comes between the alpha and the omega. This may be the perfect gift for fraternity brothers and mathematicians.

  • Your college days are long behind you, and you've made it - to New. York. City. Getting there was surprisingly easy; but getting around, well, that's a different story. Thankfully, the Dairy's "New York Subway B" case for the iPhone 6 will come it super handy when it comes to navigating the Big Apple's immense subway system. With the map smack on the back of your phone, you won't have to dig out the folded map from your wallet or miss the next train because you're staring at the station board. The price of being on time? $35, or $40 for an iPhone 6 Plus case - $5 more each for the "armored" version.