Nikiski is on the Kenai Peninsula in Southcentral Alaska.
The city of Nikiski is an oil town. Almost everything there is focussed on serving the offshore oil and gas industry. Unlike every other town in this part of Alaska, there are very few tourism based business or attractions.
To get here by road from Anchorage you will have traveled through some of the most spectacular scenery on earth. That's all behind you in Nikiski. While you can still see the mountains on the other side of Cook Inlet from here, the main thing you will see is run down strip malls, abandoned hotels, and giant petrochemical plants that seem very out of place in coastal Alaska but serve as a vital economic engine for the local economy. However, if you just keep driving for another 25 minutes or so you will reach a very nice recreation area, detailed in the next section.
Due to its large tax base from energy development, Nikiski has more infrastructure than one might expect for such a small, relatively isolated area. In addition to the building of new schools and the purchase of new fire trucks and rescue boats, Nikiski also has a publicly-owned indoor water park and pool that you can access for a small fee. About fifteen miles past Nikiski at the very end of the Spur Highway is the Captain Cook State Recreation Area. This park has a large wooded campground, a lake, and long beach along the shores of Cook Inlet. There is also road access to the beach but it is not recommended to drive on unless you have four-wheel-drive, high ground clearance, and experience driving on both deep sand and large rocks. Be aware that tides in Cook Inlet can be extreme and you may need to head to higher ground as the tide comes in. There are mudflats in this area during low tides. Do not enter these areas as they are extremely hazardous to all pedestrians and vehicles. If you become stuck the tide will eventually come back in and flood the area. The park is also the terminus of the Swanson River canoe trail. The River offers fishing for salmon on the summer months.
Since you are almost certainly coming by road, your best bet is to get whatever you need at the many stores in Kenai and Soldotna. There are convenience stores and gas stations here but that's about it.
Again, do this is Kenai or Soldotna.
You will probably want a drink when you see this town.
The way you drove in is literally the only way out unless you hire a local pilot to fly you somewhere else.