SysML-1.6/1.7: You can introduce a custom (user-defined) stereotype keyword «item» to indicate Properties that are to be used as "packets" for ItemFlows on Connectors. (SysMLv2 will have a formal way of treating such items/packets.)
This can be particularly useful when the Type of the Property is a Block (rather than a ValueType), as it helps visually distinguish these properties from other part properties in the parts] compartment.