This is what the tool grib_get_data provides: A list of latitude-longitude-value triplets for a GRIB message. Note that you can also use the API to access this functionality: See examples.
However this is only for grid-point data: For example it does not make sense for spherical harmonic coefficients.
Also it does not work for all grid types. At the time of writing only the following are supported:
- Regular latitude/longitude
- Regular Gaussian
- Reduced latitude/longitude
- Reduced Gaussian
- Lambert Conformal
- Lambert azimuthal equal area
- Polar stereographic
- Mercator
- Space view