I've handled a lot of licenses for the premium market. From Smurfs to Snoopy, from Harry Potter to Hot Wheels. Usually I would start by brainstorming a bunch of rough concepts, sketching a thumbnail of just one toy and accompanying it with a written description explaining the rest of the line. Based on their feedback I would then work up more resolved drawings defining the toy line.
Almost always there was some effort to design a connectable aspect to these, be it conceptually or literally. It created an extra level of play, but also an incentive to collect all of them.
The following concepts were proposed for some Disney premiums.
The first was done pretty early on for Winnie the Pooh, way back when I used to work entirely on the drawing board and rendering my work with Pantone markers;
Here is what the toys created when connected to form one set;
Here is another series of premiums proposed for Disney's 101 Dalmatians animated series, which premiered on the Disney Channel in 1996 and ran for 2 years. The concept here was for vehicles made up from 'loose parts' on the dalmatians property, each with its own unique track piece with a feature. Again, each premium offered some instant play, but when collected they could be assembled together for some sequential play;
Here is a sketch of the fully assembled set, creating a track that allows the character vehicles to roll through continuously;