You can regenerate your coins to their max by setting the date one day ahead in your date/time settings on your device. This can be done as many times as you desire by keep upping the date one day later than the last. You do not need to force close your device to do this. Remember to change the date back when you are done.
The most effective strategy in this game is to try to drop two or three coins at a single time, in one single roll, so that the pushing force is stronger. This will also help to maintain a straight push instead of one that makes your coin or prizes go sideways.
If you unlock the Gems collection you will get 3 coins for every one coin that you manage to collect.
If you combine the 'Straight Push' hint with the 'Gems Collection' hint you will have endless coins to play with at the end of the game. All you then need is patience and hope you are lucky and receive the prizes you don't have so you can unlock other collections.
It is not worth unlocking the Bear collections as all it does is shorten the coin regeneration by 6 seconds.
If you are lucky enough to get a whistle you will never have to worry about losing prizes that fall off the gutter. The only thing with whistles though is they do not come by often.