Especially physical things that naturally take more time implementing than it would take to pull additional ideas out of thin air, even if you just build a proof of concept.
You end up spending a lot of time thinking about things that are not required of you but are required by a project that's not required of you, and it can require incremental innovation to progress toward a rewarding milestone.
When you get accustomed to this you will be regularly thinking a whole lot more about things you would not have otherwise, and you will have some structure in place set aside in case such a brilliant idea comes along and you want to build more than a proof-of-concept.
Sometimes working without a deadline is key to actually reaching a milestone eventually, compared to unrealistic time pressure which can take so much energy accelerating up to anticipated speed, that things fizzle without going as much distance by the same future point in time beyond the deadline after all.
This is also one of those things that a lot of people are pressured to never spend time pursuing. If you do it you will be very different and so will your innovations, although without a deadline you may be at a disadvantage when it comes to extreme urgency, you can have an extreme advantage when urgency is not the utmost consideration.
Sometimes you just need to get out and breathe a little fresh air.
Combining innovations e.g. fork chopsticks.
Transfer, e.g cement mixing in non-stick kitchen tools.
Stealing and improving, e.g. offering the same thing in a different color.
Sort the unsolved problems along a priority list important to you or others?