Is there a way for people to scan my QR code and send me bitcoin in face-to-face situation? I won't have access to 3g or wifi but they will have 3g internet access.
1. Before they scan, they would need to download an app or something else?
They would only need a mobile Bitcoin wallet of course. Most mobile wallet already have QR code reader built into their apps, so no additional app is needed.
2. Do I make a sceenshot on smartphone (Samsung), are there alternatives to carrying a printed paper version of my QR code around?
Thanks
Yes, you can screenshot your address QR code. It will be valid forever. Alternatively, you just need to save your Bitcoin address on a note, then generate the QR code using online block explorer service like blockchain.info or blockexplorer.com. Most online blockexplorer website would show the QR code when you search for an address.