It sounds like a nice idea, but I wouldn't fill it with "diet" snacks like skinny whip and fibre ones.
Actually I think Options sachets could go either way - they're one of the more common single serving ones I see. If you filled the bowl with diet snacks it would feel like a diet food, but if its filled with "normal" snacks, it would come across as just what they had in Tesco, rather than the "healthy choice"
That's not to say you need to go straight to full size chocolate bars, and packs of crisps.
Perhaps "lunch box" biscuits - like rocky or clubs, possibly some more cereal bars - brunch bars or similar.
I'd be very happy with latte or cappuccino sachets
Of course, the best thing is to ask them what they'd like in the bowl - if skinny whips etc are their thing, go ahead. Perhaps unnecessarily - if you get guests in your office, it might be worth chucking in something not "diet" in case they interpret it as a secret dig.
Fruit bowls are nice if they'll get eaten - but won't last nearly as long as snacks.
Moot point, as it sounds like they like the idea, but I'd rather not have a snack bowl, but a weekly/month treat with a "fresh" snack - like pastries or cake.