1. they could meld the treasure-hunt aspect of Pokemon Go with sponsored hyperlocal recommendations. ARGs (alternate reality games) are popular with Snapchat's core demographic, and if Snap could pitch itself as a platform for ARGs, their advertising woes would disappear.
2. microtransactions familiar from Asian messaging apps: cosmetic stuff like stickers, emoji packs, backgrounds, filters, etc
3. (macro-)transactions for large-scale content inside of Snapchat. Facebook had entire video games playable within it; there is no reason Snapchat can't do this. There is a market for VIP access for 'private' Snapchats of celebrities and creators, but today this is arranged out-of-band, because Snapchat provides no support for this in-app. Patreon was able to make headway in this underserved market.
4. Snapcash could compete with Paypal, but it's vastly overemphasized.
5. Snap Map has so much potential, and it's unexploited. From mundane to exotic, opportunities include location search, sponsored recommendations, user-generated content about real-life places (cf. Yelp), user matching for transactions (cf. Uber), user-generated content anchored in virtual space (AR stuff)...
6. Subscriptions. Either to gate specific content or features, or just for the sake of. Discord has a sponsor tier that gives a few perks but is just as much for the sake of providing support. There is always a subset of users who will pay.