Take the sentence in the title for example. In French one might say something like je le prends or je l’apporte. In Italian the closest equivalent might te lo prendo (io).
The main difference is that both languages would use the present tense (and both basically only have one present tense each). And that makes sense, because if you say something like I’ll just get that for you now, you’re talking about the present, aren’t you? Sure, you’re using will, but that doesn’t mean you’re talking about the future: you wouldn’t also put now at the end if you were, would you? But then if it’s clear that we’re talking about the present, why not use a present tense, instead of will?
English has quite a few after all: why not use one of those? Well, the present perfect simple and continuous wouldn’t really work, as they require some link to the past. The present simple wouldn’t really work, because we only really use that for states or regular actions.
Now the present continuous, that feels like it really should work. We use it to refer to the immediate present, something currently in progress. But… I’m getting that for you now. Doesn’t really work, does it? Mainly because we’re not talking about something in progress. Yet.
Strictly of course, it really is a future event we’re referring to, one that’s about to happen, rather than happening now. But it’s so close to the present that the distinction between present and future is really academic. Which is why most languages use the present tense.
But not English. I think that’s partly down to the language’s tendency to impose distance, and push things away. By pushing the action into the future, we’re making sure we don’t get too close to the person we’re talking to.
Still, I find it very curious that for all the English language’s versatility, and its abundance of present tenses, it can’t use any of those present tenses to refer to an immediate, individual action. But I think things could change further down the line. Non-native speakers of English outnumber native speakers, and I’ve already looked at how they’re helping to shape the English language. I imagine in the not-too-distant future, we might find ourselves saying things like I get that for you now.