$0.99? I was thinking more like $2.99 or so.

Who buys consumable IAP to support app authors anyway? I've never heard of that. Buying single-use IAP like ad-removal or coin-boosting, yeah, people do that to support the authors (I'll do that if I think it's a game I'm actually going to play). But that really only applies to single-time purchases, not consumables.

And yeah, you can add cosmetic stuff like themes, or character costumes, or other non-gameplay-affecting things. That's a decent way to provide an opportunity for people to give you money without making them feel like they have to pay to play (you can even make this stuff cost coins, but set the price a bit high to encourage people to use IAP to afford it (but no so high that people think it's unobtainable without IAP), or have a few "special" items that are IAP-only).

Basically, the best approach IMO is to have virtual currency (coins), that you can earn through gameplay, or purchase with IAP. These coins are used to buy things that are perhaps purely aesthetic, or nice-to-have, but are not required in any sense for actual gameplay, or to be able to get a good high score when competing with friends. For example, in a Ski Safari-style game, you might purchase boosters that deposit you partway into the level; you could certainly get that far on your own, so it doesn't affect your high score, but it skips past the "boring" speed ramp-up and so gets you into the action a bit faster. And since these are purchased with coins instead of directly with IAP, people can still play around with them without spending money, which of course provides a way to use up coins and therefore encourage them to buy more.

Once you have these coins, I would then recommend a single permanent IAP purchase for some form of coin booster, as I suggested before. This provides the easy option for someone who wants to support the game author (and therefore feel like they paid for the game), while at the same time giving them a permanent reward for doing so. Not only that, but because it's a permanent reward that they just spent money for, it then becomes a sunk cost if they stop playing the game, and so it's a subtle encouragement to keep coming back to the game, to make sure they got their money's worth. This works the same way as when paying for a game outright, of course, but the alternative, of just relying on consumable IAP, does not have this property because, of course, once they use up what they bought, they've already extracted all the value they could from the purchase.

Finally, I would suggest avoiding ads if you can get away with not having them. Ads are tacky and ugly and will cause a lot of people (myself included) to not even put in the time to find out if the game is any good. But if you decide you need ads anyway, make the coin booster also disable ads at the same time.

Also, as I said above, a coin booster IAP like this seems more like $2.99-$4.99, not $0.99. The nice thing about having it be IAP instead of an upfront cost is that once people decide they like a game, they're more willing to pay more than a dollar for it. The $0.99 price for a lot of games is like that because people have to pay upfront, and it's hard to convince someone to pay more money when they can just go buy a cheaper game. But once they've already decided they like a game, it's easier to justify the higher price.