Necessity is the mother of invention and in Dr. Stone, their needs are sky-high since civilization was reduced to stone-age tribes and only one man can rebuild all of it. That would be Ishigami Senku, the only supergenius in Dr. Stone who managed to memorize seemingly all invention formulas to rebuild everything from scratch.
It's not an easy task and Senku has proven many times over that his intellect nor his logic isn't bulletproof. While most of his inventions are incredible and beneficial and can fast forward mankind's advancement, some don't exactly scream practicality given the situation. So while Senku does have some essential inventions, he could have saved time and resources by inventing something else.
10 Useful: Antibiotics
Prolonging human life should always be the number one priority of one who is looking to raise a civilization. It just so happens that diseases are the number one culprit in reducing human life expectancy. Senku's tribe seems predisposed to be afflicted with pneumonia and thankfully, he answers that problem well with antibiotics.
To be more specific, that would be the sulfa-drug he invented from the chemicals and minerals he could collect in the environment. By inventing medicine, Senku already has a clear advantage over the rival tribe led by Tsukasa as those guys merely rely on physical fitness alone to prolong their lives.
9 Impractical: Katana
Before joining Ishigami village and eventually becoming its chieftain, Senku has already invented something better than a melee weapon: a crossbow. Tsukasa was the only one who could catch crossbow bolts anyway. So why the need for a katana?
Senku's claim that katanas are the best swords ever invented is also a bit biased; katanas aren't exactly the best weapons for defense. They're more designed for cutting and killing enemies, and since Senku doesn't want to resort to bloodshed or violence, double-edged swords or even pikes would have been more superior. Really, crossbow shooters behind a shield wall would do the trick.
8 Useful: Gunpowder
One of the reasons why Tsukasa was so scared of Senku was gunpowder. After all, the existence of guns pretty much made all humans equal physically. Guns or gunpowder-based weaponry would have nullified Tsukasa's physical advantage.
It was by far Senku's most important invention when Tsukasa started becoming hostile. Apparently, he still can't mass produce it since the best source of gunpowder ingredients is guarded by Tsukasa. Still, in a world where a stone spear is the most practical weapon, gunpowder might as well be a superweapon.
7 Impractical: Steam Automobile
Senku skipped the carts and wagons and went straight for a tank, a steam tank of all things. It's one of the highlights of Season 2 of Dr. Stone; Senku makes it his ace in the offensive against Tsukasa except he mostly planned to use it as a one-shot weapon.
The tank was made to function like a ram that will crack open Chrome's prison for a daring escape, except Senku didn't even need something as elaborate as a tank to do that. He could easily make some explosives with the spare gunpowder he has. That also would have been less conspicuous to transport given the terrain of the Stone World.
6 Useful: Electrical Generators & Storage
Electricity or energy is the glue that keeps the modern world, well, modern as many things rely on it. Senku knew this very well and made some generators to enable many other inventions and reduce the amount of manual labor the village needs for his inventions.
It not only allowed them to have light even at night but also many other luxuries we enjoy today. The village even went above and beyond and made batteries. With that kind of technology, they could have made tasers and even shock batons.
5 Impractical: "Cellphone"
It seems Taiju's bluntness might have rubbed off on Senku because he kept referring to the walkie-talkie as a cellphone. It's true that long-distance communication would have turned the tides of modern warfare, but Tsukasa isn't even there yet and will likely never get to that point.
To that end, the cellphone/walkie-talkie is a bit overkill as a strategic advantage. Senku doesn't even need that much information about Tsukasa's movements as the Ishigami's weapons will always be ages ahead. Senku could have made crossbows, iron shields, tear gas, and many other non-lethal means of subduing Tsukasa's stone-age army. Instead, they wasted the whole winter making a walkie-talkie.
4 Useful: Lenses
The human eye is probably the most important or most valued sensory organ these days since the brain functions best when fed with visual information. In a setting such as the Stone World in Dr. Stone, having poor eyesight might as well be a death sentence.
Senku managed to fix this problem quite quickly by making some corrective lenses. Though to be fair, half the credit goes to old-man Kaseki for having the skills and expertise to handcraft lenses which can also be used as a telescope for spying.
3 Impractical: Ramen/Instant Ramen
Senku's reasoning for not attacking during the winter season in the anime is that food can easily become a logistical nightmare and disaster. He's right for the most part but his solution is a little convoluted and overly complex: instant noodles or ramen.
He didn't even need to go that far. All they had to do was smoke or dry some fish or boar meat and they have food that can last for long periods and provide nourishment. If they need warmth, then hot water ought to do the trick. By contrast, instant noodles take more time to prepare and make more mess. It's wartime anyway so they shouldn't be looking for the luxuries of flavor.
2 Useful: Revival Fluid
By far the most invention Senku has ever made was a product of nature that he improved. That would be the miracle fluid that de-petrifies every victim of the Stone World. It was the key to ensuring that remnants of the old world can still be carried over to the new one.
The ingredients were even simple enough and probably abundant enough that Senku doesn't need to compete with Tsukasa for the deposit. There ought to be another bat cave nearby brimming with guano and nitric acid.
1 Impractical: Cola
Cola or carbonated drinks might have been impractical in Senku's Stone World but that doesn't mean it's entirely useless. Cola was a Gen's special request for ensuring his loyalty to Senku but really, it was unnecessary.
Gen was already enamored and impressed by Senku as an individual before he even met the genius. Senku probably knows that too but Gen was lucky that the ingredients for cola were available along the way as they were making the antibiotics.