Voluntary Public Access Improvement Act of 2018 This bill amends the Food Security Act of 1985 to increase and extend through FY2023 the authorization of mandatory funding for the Department of Agriculture Voluntary Public Access and Habitat Incentive Program. (The program provides grants for state and tribal governments to encourage owners and operators of privately-held farm, ranch, and forest land to voluntarily make the land available for access by the public for wildlife-dependent recreation, including hunting or fishing.)