This may already exist in the form of a collector's book with all the field data. If the only data are on the packets, it is a good idea to re- create a field book by noting number, name, locality, habitat, altitude, date, etc. in columns on sheets of paper or in a new notebook which forms a reconstruction of the collector's field work. I find this last approach very useful and keep special hard-backed notebooks for miscellaneous collections given to me. For large or inadequately dated collections such an approach may be impossible or difficult, but at least a list giving collectors number and plant name in columns will be useful for the archives of the herbarium holding the collection. Some collectors use 'blank' labels pre-printed with country, year, collector etc.
Data are typed in, then the label is copied for duplicates and glued to folded packets.
With word-processing such labels are becoming increasingly redundant as label data can be printed easily on to unfolded packets. Make sure to leave at least two lines for the name. The actual division of material should ideally be delayed until after identification, but if the specimen is bulky it may have to be split sooner. Take care that duplicates are adequate as specimens in their own right, tiny scraps are almost useless.