I'm still not sure you are getting what he is driving at.
My Linux setup with Bitcoin-QT installed created a .bitcoin folder inside my home folder. It's current size (bitcoin-qt is running and current) is 9.4 GB.
Of that, the wallet.dat is only 92 KB in size. The rest is the blockchain data...
I totally get this. However once I have the wallet.dat encrypted on my flash, I can use any client to for accessing it, can't I? The software client is no problem. I can change it to a lighter version. What would you suggest? My problem is to trust any third party code (Armory, i.e) in this. That's why I wanna keep it really simple.
Please also let me know if I understand correctly that the wallet.dat is only thing that matters? The client can be changed afterwards.
wallet.dat is only used by bitcoin-qt. Other clients like armory or electrum have their own different wallet formats.