What is the meaning behind 5000萬「袋住先」and D7689!@#?
The pronunciation of "D"-"7" is similar to a Cantonese foul phrase (something similar to  fxxking hard).

689 is a common way to refer to the current Chief Executive (CE) of Hong Kong, because he won the election in 2012 by having 689 electoral votes out of the 1200-person Election Committee.

"袋住先" is also a common Cantonese saying.  "袋" here means the action to put something in your pocket, as analogous to "acceptance".  "袋住先" is to accept something at the time being, with a implicit promise that something better will be offered later.

Hong Kong would probably be having an electoral reform to adopt universal suffrage in 2016 CE election according to the Basic Law (supplemented by elaborated explanations from the Standing Committee of the National People's Congress of China).  The HK Government is promoting its Beijing-blessed proposal and many famous people are telling the citizens to "袋住先".  (This is IMO somehow self-contradictory because the proposal is advertised as "universal suffrage" and the Basic Law does not mention any improvement beyond "universal suffrage".)

As for "5000萬", please refer to http://www.theage.com.au/business/world-business/hong-kong-chief-executive-cy-leung-faces-questions-over-secret-7m-payout-from-australian-firm-20141008-1134yv.html