Happiness ahead...You will be rich - you will be able to afford pudding for supper [ashore] with your share of the cargo. Now row.
There is also a reference to copulation [another enticing reward!] at have hot pudding for supper I have not read enough Melville to know the extent of sexual imagery in his writing.
Several paragraph earlier there is a lengthy example of Stubb's exhortation to his crew followed by a narrative description of his method.
"...Pull, pull, my fine hearts-alive; pull, my children; pull, my little ones," drawingly and soothingly sighed Stubb to his crew, some of whom still showed signs of uneasiness. "Why don't you break your backbones, my boys? What is it you stare at? Those chaps in yonder boat? Tut! They are only five more hands come to help us - never mind from where - the more the merrier. Pull, then, do pull; never mind the brimstone - devils are good fellows enough. So, so; there you are now; that's the stroke for a thousand pounds; that's the stroke to sweep the stakes! Hurrah for the gold cup of sperm oil, my heroes! Three cheers, men - all hearts alive! Easy, easy; don't be in a hurry - don't be in a hurry. Why don't you snap your oars, you rascals? Bite something, you dogs! So, so, so, then; - softly, softly! That's it - that's it! long and strong. Give way there, give way! The devil fetch ye, ye ragamuffin rapscallions; ye are all asleep. Stop snoring, ye sleepers, and pull. Pull, will ye? pull, can't ye? pull, won't ye? Why in the name of gudgeons and ginger-cakes don't ye pull? - pull and break something! pull, and start your eyes out! Here! whipping out the sharp knife from his girdle; every mother's son of ye draw his knife, and pull with the blade between his teeth. That's it - that's it. Now ye do something; that looks like it, my steel-bits. Start her - start her, my silver-spoons! Start her, marling-spikes!"
Stubb's exordium to his crew is given here at large, because he had rather a peculiar way of talking to them in general, and especially in inculcating the religion of rowing. [...] He would say the most terrific things to his crew, in a tone so strangely compounded of fun and fury, and the fury seemed so calculated merely as a spice to the fun, [...] Then again, Stubb was one of those odd sort of humorists, whose jollity is sometimes so curiously ambiguous, as to put all inferiors on their guard in the matter of obeying them. ..."
A little later in the chase Starbuck reminds Stubb that despite the unease surrounding Ahab's crew they have a job to do.
"There's hogsheads of sperm ahead, Mr. Stubb, and that's what ye came for. (Pull, my boys!) Sperm, sperm's the play! This at least is duty; duty and profit hand in hand!"
Your quoted passage broadly parallels Stubb's earlier one staring at "Merrily..."