The quickest, safest, and easiest way to make sure you backup all you need is to follow these simple steps:
0) Make sure your wallet is encrypted! This should have already been done anyway so it's step 0
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1) Shut down your client
2) Find your wallet.dat file (in %AppData%/Protoshares or /home/<user>/.protoshares)
3) Copy your wallet.dat to another location and called it pts_wallet.dat or something similar so you don't confuse it with your XYZcoin.dat wallets. For example I have pts_wallet.dat, ftc_wallet.dat, ltc_wallet.dat, btc_wallet.dat, etc. etc.).
4) Put the USB stick or whatever you copied it to in another physical location (in a drawer at work and/or home, your garage, etc.). Somewhere that can be accessed if one location burns to the ground, gets wiped out by a plague of locus, etc.
5) Restart the client.
6) Rinse and repeat about every 100 transactions to make sure your backups have all your latest change address key pairs.
Depending on your level of trust in online storage solutions you could rename the pts_wallet.dat file to something like mittens.jpg and put it in the pictures folder of your Google Drive or other service. Since it's encrypted it's reasonable safe from theft (though technically not totally safe) and renaming the file would save you from quick scans by someone who hacks an online storage site and scans for wallet.dat files.
The wallets are really really small. On most $10 USB sticks now you could even back up the entire blockchain if you wanted to save yourself the time of downloading it again in the future but it's not required. Your wallet.dat file is like your SIM card in your phone. Everything else is generic software.