I’ve used real Smilax sarsaparilla root, which is pretty hard to find. The good stuff, anyway, is scarce. Its flavor and aroma are most similar to vanilla. Root beer is called sarsaparilla in some countries, and the mockups of “sarsaparilla” concocted here are just versions of root beer. The most characteristic flavor of root beer is that methyl salicylate again, primitively derived from birch bark and wintergreen. Combined with sassafras flavor, and vanilla flavor to stand in for the sarsaparilla, there’s your root beer.
I’ve had some wheat beers (Brooklyn specifically comes to mind) that had a bubble gum flavor.
For what it’s worth, I’ve always thought that both Red Bull and Southern Comfort tasted exactly bubbly-gummy. Vile stuff, both of them.
That would come from the esters/phenols the yeast strains used in many style of wheat beers throw off. Banana and clove flavors are pretty common in wheat beers – those are from amyl acetate and 4-vinyl guaiacol respectively. I find German-style hefes to be more on the banana-y side, and the Belgian being more on the clove side. Some people perceive these flavors as bubblegum, too (which makes sense, as it seems banana+citrus/orange is what many people in this thread are ascribing to the bubblegum flavor. I tried the bubblegum cocktail mentioned upthread and was surprised at how close to bubblegum it tasted to me. Those two flavors seem to be the key.)