#1 - Rixie Clip
#2 - Band Extender
There are lots of options available, including these $2 ones from Motherhood.
#3 - Bra Strap Clip
#4 - Cup Insert
Inserts are also good if you've lost some weight in your breasts, but you don't quite want to re-buy all your bras. $10 soft inserts can help extend the life of your existing bras without having to get smaller ones just yet.