All good stuff that has been mentioned, Samoa Cookhouse is a must with a group, it is great food served family style and more if you want it. Fort stevens is a wonderful park, bring or rent bicycles lots of trails, look for the pillboxes and bring a flashlight for the old fort.
At Florence, Jessie Honeyman state park is similar plus you can get a dune buggy ride or rent quads to ride the sand dunes, also at the beach.
It is the top of ODNRA- Oregon Dunes National Recreation Area the area spans to Coos Bay. There is an off-road section at Florence then a section closed to OHV's, you be able to figure it out.
It is where there are no footprints or tracks,who is going to walk miles in the sand to the beach? Stupid but that is our US Forest Service providing for... who?
Next comes Salmon Harbor just south of Reedsport a really nice place for day-tripping and going on a fishing charter, has some very nice RV campgrounds. Also just around the corner is Winchester Bay the center OHV area partly controlled by the Forest Service but THANKFULLY the Douglas County community understands the importance of dollars spent by the OHV users that supports a great deal of the local economy.The County puts on Oregon's largest OHV event in August called DUNEFEST, I have volunteered as a Camp Host for several years. It is a family oriented event that has lots of appeal and is kid oriented, quad rentals are available there too.It has the largest dunes and is very scenic, no beach riding there.
Moving farther south is another area closed to OHV's, there are several campgrounds both State and private next to lakes in the vicinity.
about 8-10 miles south is the last area open to OHV and is the largest riding area it stretches from Spinreel to Hauser to Coos Bay. There is beach riding there too, and at Hauser is a KOA with a rental nearby.
Have fun in Oregon, you have to try real hard to not have any!