You can modify following code to fetch all fields of your item:
var list = _clientContext.Web.GetListByUrl(<ListUrl>);
var query = new CamlQuery
ViewXml = @"<View><Query><Where><Eq><FieldRef Name='Title' /><Value Type='Text'>Home</Value></Eq></Where></Query></View>"
var listItems = list.GetItems(query);
GetListByUrl() is extension method from Office PnP Core library - if you do not use it, you can replace it with following code:
In provided sample I was filtering by Title field - if you specify your query as follows:
var query = new CamlQuery();
you will fetch all items and all of their fields.
Hope it will help:)
Getting items with IDs only can be done this way:
var query2 = new CamlQuery();
var listItems2 = list.GetItems(query2);
_clientContext.Load(listItems2, items => items.Include(i => i.Id).Where(i => i.Id == 1));
Where statement can be removed if you want to get all items with theirs' ids. This approach is a bit different than previous one - I do not use ViewXml of CamlQuery, but output is exactly the same.