A striking aspect of English as spoken by many from Wisconsin and Minnesota is that the vowel /æ/ (like in had, sad, bad, etc.) is changing or has already changed dramatically before /g/ (as in bag, flag, nag). It raises (to [ɛ] or something close) and often tenses (to [e:] or less monophthongal variants), with a lot of movement in the vowel. In the "Northern Cities Shift", /æ/ changes earliest and most notably before sounds like d and t and last before velars like g, according to Labov et al.'s Atlas of North American English. But here, it's before g (and k and ng for some people), and only later before alveolars like d. The stereotype here is that when asked if you want a bag for a couple of items in a store, it sounds like you're getting "wanna beg for that?"
One of the few really negative reactions the Wisconsin Englishes crew has gotten from the press and even other specialists has been to their seemingly uncontroversial note that bag in Madison often sounds like beg to outsiders. (Only somewhat less controversial is that bag can come to rhyme with vague.) This cartoon shows the perception of bag pronounced as beg by, I assume, a speaker: The cartoonist seems to be from Canada, where Labov et al. report this pattern.
So there. And thanks, Kevin!
(If you can't see the cartoon well enough, go here.)