I'm going to go with:
1. Carbon tax (as in CO2-burning, or other greenhouse gases like methane), to provide a financial disincentive for contributing to climate change, hastening the switch to cleaner energy and non-gasoline cars, while also raising government revenue.
2. All illegal immigrants are now citizens, unless they're murderers or rapists on the run or repeat offenders or something. They can pay taxes, can actually talk to the police without being at risk of being deported. They were already doing jobs (or they'd have left), now they'll contribute to the tax base, can vote, and can't be exploited as easily. This may have knock-on effects (on the economy, or on immigration), but I feel it's the right thing to do. We also shouldn't be deporting all those refugees fleeing murder from south/central america either, or holding them in internment camps for months.
3. Legalize, regulate, and tax prostitution. (I wouldn't use it myself but I don't see any reason why it should be illegal, it just drives it underground)
4. Legalize, regulate, and tax marijuana. We already have alcohol and cigarette taxes, of course.
5. Alter the criminal justice system to be focused on rehabilitation rather than punishment.
6. The education system needs to be revised, and everyone agrees on that, but nobody agrees on how. So I would ask folks in the Scandinavian countries what theirs is like and if it would work here. (The teachers would all need retraining, and it would need to be free, though, but they could do it on the internet, which would help with the cost and eliminate travel time)
7. Public colleges shouldn't cost anything. Some European countries have figured this out. We can probably copy how they did it.
8. Cut military spending, by, for example, getting rid of all our ICBMs (which would have a one-time cost but eliminate the continuing cost of upkeep), and cancelling the F-35. I'd also keep the A-10 warthog. If it's expensive because of old components, perhaps have a new model designed that uses more modern components that are easier to acquire. I'm speculating on that. I don't know why they're cancelling it instead of updating it. They don't have anything else that can do the same job as well.
9. Instead of investing in fancy new planes, fund work by the NSA and/or DARPA to find ways to hack potential enemy planes (and secure ours). If possible have satellites able to hack in and take control of enemy planes, or if not, drones to do it. May also need to develop stealth drones. Once hacked they're probably vulnerable to all kinds of stuff. Like screwing with the flight systems to cause a crash. Maybe ejection is available, but I wouldn't be surprised if it was just a button/switch that the computer(s) had no access to.
10. There are far more deaths due to heart disease and cancer than gun violence, so to avoid antagonizing half the population I would mostly leave the gun issue alone, and instead fund further research into both heart disease and cancer, and aging.
11. There's still an epidemic of drugs and "drug abuse" which has been in black communities for a long time, and is to my knowledge only recently getting widespread mainstream media attention now that it has reached suburban white communities (they're reporting on heroin currently). Legalizing heroin or other highly addictive drugs isn't the answer because of how addictive they are. Considering supply and demand, I would expect that as long as the demand continues, supply will try to fulfill it. If there's excess supply it will try to create new demand (addict new people). So far efforts have focused primarily on cutting lines of supply or making it harder to create (e.g. for meth) but as long as there is profit to be made it will keep coming back. So we need, first, a program more effective than DARE at convincing young people that (addictive) drugs aren't cool, that they aren't designed to be awesome, they're a way to turn you into the most reliable repeat customer there is by turning you into a slave to your addiction (and that people sometimes die of overdoses or an impurity in their drugs, but since addicts run out of money and things to sell and often can't hold down a job, they become less and less useful as customers, so they don't really care that much if you die). The point is to eliminate the future customer base. If a medicine is developed to cure addiction permanently, that would also help current generations that want to quit to do so.
12. Let Daesh know we're going to bring our armies to Dabiq to meet them on the field of battle. Send transports and such with genuine imitation tank drones, i.e. the cheapest thing that appears to be our tanks but is actually a treaded drone in a tank-appearance shell. Not that they have satellites or anything. Unload them and send them to Dabiq. When Daesh's armies all show up, drop a nuke on them, breaking their prophecy and their armies.
I'm sure there could be more but I doubt anyone wants to read even more stuff.