This is the proof version of the Australian circulating coin set for the year. It contains all the regular circulating denominations from $2 down to 5 cents. Instead of the regular (definitive) 50 cents though, the set contains a coloured 50 cent coin commemorating the 50th anniversary of the Australian honours system.
The mint says about it:
First introduced in 1975, the Australian honour and awards system is a uniquely Australian way to celebrate those how have made a positive impact, with more than 500,000 people having been recognised since their introduction in 1975. The Royal Australian Mint acknowledges five decades of Australian honours and awards and their inspirational recipients with this striking commemorative year set.
The set features a specially designed coloured 50c coin, based on Stuart Devlin’s iconic Order of Australia medal, incorporating the ribbon colours of the Order of Australia, Bravery and National medals. | 
Search for this coin set on eBay 