If you are just talking about Classic, there are a few options. Blitz/Thresh while landing hooks are good choices. I would say Blitz over Thresh since you can hook and blow up a squishy, Thresh needs his team to follow him up or he'll prolly die (like Leona). Nami also isn't bad for this. I've been practicing with her and if you are aggressive with your bubbling (and later bubble + ult) you can bullying during lane phase + ruin enemy plans during a teamfight.
The other option is to start support then build into more offense. Zyra, Fiddle, and even Karma/Morg/Orianna can do this (and prolly even more). Get a Sightstone for some ward coverage, then Chalice so you can spam abilities more, then whatever works best for the champ in question (always get some wards of course). It's not always ideal, but if your team is terrible buying things like Bulwark/Shur aren't going to mean much, and it's common for a jungler to get Bulwark/Locket now anyway.
I've won quite a few games with Nami recently, but haven't always had a great carry. For example, an Ez and I had a pretty great laning phase, but then he wanted to spend a ton of time roaming for no reason, even leaving our bot tower to lose 80% of it's HP just from creeps, even with me pinging repeatedly and clearing them myself. In situations like that, follow/support those who are functioning properly: a support can still turn a losing duel into a 2 vs 1, and catching 1-2 team members out and staggering their respawns can mean a few towers or inhibs under your belt.