First find the number of spiral shells Jackson collects: 45 hermit crabs * 3 spiral shells/hermit crab = <<45*3=135>>135 spiral shells
Then find the number of starfish he collects: 135 spiral shells * 2 starfish/spiral shell = <<135*2=270>>270 starfish
Then add the number of each animal he collects to find the total number: 135 spiral shells + 270 starfish + 45 hermit crabs = <<135+270+45=450>>450 souvenirs
#### 450