Let's see… where to begin? Well, the obvious is a good place to start. It's pretty easy to tell that our speaker is feeling more than a little put out by the whole toad-work thing. Those exclamation points that keep popping up tell us that he's feeling fairly passionate about the injustice of it all: "Just for paying a few bills!" "Stuff your pension!" But there is more to this guy than just being a little hot under the collar.
First of all, it doesn't seem like this is the first time the speaker has thought about this problem. This is something that has been building up for some time. He probably isn't seventeen and toiling away at his first fast-food job. It feels more like a middle-aged guy that is trying to come to terms with what his life is going to amount to.
We also get the sense that this speaker is being honest with us. He admits to having that internal "toad" after all—that has to be a little embarrassing, right? It's one thing to have an internal unicorn or perhaps an internal Jedi master, but a toad?
It can be pretty boring listening to someone complaining, going on and on about this problem and that. But we don't really feel that way with this speaker. He isn't whining and griping (or "whinging," as our British friends like to say) just to hear his own voice. He seems like a guy that just can't see his way clear to a solution and you might even feel a little sympathy for him (we do anyway). The sad thing is, even after his little rant, he doesn't seem any closer to solving his problem. If anything, by the poem's last stanza, he seems resigned to the fact that his toads (internal and external) aren't going anywhere.
Finally, the speaker seems educated but not pompous. He's familiar with Shakespeare ("that's the stuff / That dreams are made on") but he also knows how regular, down-and-out folks live ("up lanes / With fires in a bucket").
While it is always a good idea to separate the speaker of a poem from the poet, this speaker does seem to share a certain bleak outlook with the poet himself. Larkin, like this speaker, didn't really have a rainbow-y perspective on life. Check out "Calling Card" for more on that.