I am very late to this party ... I just bought an UNO WiFi and I am looking at creating a simple protocol to persist data with a data store on another device connected to the WiFi. Probably will use HTTP with simple end points, treat the remote storage as a contiguous memory block:
GET IP:port/addr/len
PUT IP:port/addr data
I could also create named blocks (think files):
GET IP:port/name
PUT IP:port/name data
The actual remote storage could be anything, memory mapped disk file, SQLite3 database, etc.
There are many drawbacks, such as reliance on the external service, connectivity issues, error handling, etc. I could run out of code space just supporting the protocol.
EDIT: I got a little flack for my answer, including downvotes, however, read the OP - he stated "somewhere" for retrieving variable data; a LAN device certainly falls in the category of "somewhere", especially when the UNO has WiFi. My answer might not be suitable for the OP, however, after reading my answer, the OP might opt to get a WiFi enabled device. I do not believe in "keyhole" solutions, but rather to provide options that fit the general tone of the question even if it means getting out of its box.