a) Flowers. OK, that's what we expect - they're a symbol of the fleeting nature of life.
b) A reproduction road sign, for Stamford Bridge. OK, that has meaning, the dead teenager was a Chelsea fan.
c) Cans of Red Bull and bottles of Lucozade. Hmm, well, there is a long history of libatory drinks, and given the driver was apparently drunk, alcoholic ones would have been inappropriate.
d) A shrink wrapped ball of string.
Yes, you read that right. A ball of string, still in its polythene wrapping.
Perhaps that last one just fell out of a shopping bag while the owner was laying something else.