Check this out. Soil sampling plan creation. The basis could be any zones (for example based on yield, soil, topography, historical imagery - example).
It manages all the aspects of sampling, including creating of labels for lab. And then import of csv/excel becomes effective even in composite per zone sampling case. 

You can also export the map to Ops center (as workplan, or map layer or Files/vra). 

In regards of flags, can't help you with that right now (need to check it out), but in case you use the approach, you can also you the mobile app for sampling.