please give alternatives for someone like me who's always on the go.
Bring your own laptop, or buy a small lightweight laptop for your travels. Netbooks weigh 1 kg and don't cost much.
Don't carry around all your crypto holdings, bring only what you need for your trip, and leave the rest in secure storage elsewhere.
Generally speaking, you can rely on your hard drive for three to five years on average.
Obviously, you'll need to make backups. You should be able to lose your portable device at any moment without losing any coins.
If you're worried about security, learn something about paper wallets and you'll be fine.
I have a BIP38 encrypted paper wallet in my wallet, it used to be worth enough for a tank of gas, by now it holds enough Bitcoins to buy an average laptop.
For wallets, I prefer to use my PC, but for mobility, I also have Mycelium installed on my phone. The paper wallet in my wallet is much more secure than my phone, and I'll only touch it if I ever need to use it.
I don't see any problem with storing your wallet files on an external hard drive, assuming you take the proper precautions when securing the drive itself.
You could bring a Linux LIVE DVD, or even make the external hard drive itself bootable. That way, you can quite safely use it at any computer, but I don't think many people would let you use their computer to startup your own OS.
But I wouldn't let anyone plug his USB-drive into my PC to start up his own wallets anyway.