On Saturday, April 13, Robert F. Kennedy held a campaign meeting in Iowa, in order to get on the ballot without the need for a petition. Iowa lets independent candidates, and the nominees of unqualified parties, get on the ballot if they have 500 voters at a meeting. The Kennedy meeting had 686 eligible voters, so he has essentially completed his ballot access work in that state. See this story.
The method is very seldom used. A few years ago the legislature increased the attendance requirement from 250 to 500.
At the Iowa event, Kennedy said he is no longer interested in the Libertarian nomination.