One of The Shortest method i found for single value while i was searching for myself, is just passing single string and setting string as model in view like this.
In your Partial calling side
@Html.Partial("ParitalAction", "String data to pass to partial")
And then binding the model with Partial View like this
@model string
and the using its value in Partial View like this
@Model
You can also play with other datatypes like array, int or more complex data types like IDictionary or something else.
Hope it helps,