I like to play around with different ways to finish untreated wa handles.
What I like to do the most is dip the handle in boiled linseed oil for a few days. Then let it dry for a few days to a week. When it's dry I'll buff. It'll darken the colour a bit, but I like the protection it provides. The long oil bath helps the oil to really seep in and helps to treat the wood and prevents it from drying. There are some stuff that start to wear it off like fish oils and acidic juices. When the surface starts to feel dry just repeat the process.
You can also just apply a few layers of oil and buff in between. It works OK, but the protection is a bit weaker. The colour of the handle will stay lighter this way.
Sometimes I'll add on top of the oil treatment a couple of layers of beeswax and buff, let dry and buff again to a high shine.
You can also just apply the beeswax without the oil treatment. It will change the colour the least. It'll hold for a good while, but can slowly wear off. Acidic stuff and fish oils will afflict it's ability to protect the wood.
The already mentioned tru oil works in a similar way to boiled linseed oil. So does tung oil.
On one handle I put on a crazy glue finish. It works similarly to a lacquer, it just makes a harder surface. The glue won't dry when applied as long as you don't let it sit so keep it moving. after few layers I sanded it with a couple of high grit sand paper and buffed it to super high shine. It's held on really well for about three years now and still is as good as the day I did it.