Column with arbitrary located byte in a packet

This is (currently) not possible with Wireshark, although you might be able to do this with the Lua scripting engine that is part of Wireshark.

"use the Code, Luk"
add the Custom "udp_dump.data" column in Preferences/Columns and tweak protocol port and byte offset in Preferences/Protocol/UDP_DUMP. Upvote! =)

do
        local udp_dumper_proto = Proto("udp_dump", "UDP dumper");

        udp_dumper_proto.prefs.ofs = Pref.uint( "udp_dump_ofs", 1, "UDP data byte offset" )
        udp_dumper_proto.prefs.port   = Pref.uint( "udp_dump_port", 53, "UDP port" )

        udp_dumper_proto.fields.dump   = ProtoField.uint8("udp_dump.data", "a dump of byte", base.HEX)

        local prev_proto
        local f_udp    = Field.new("udp")

        function udp_dumper_proto.dissector(tvb, pinfo, tree)
            pcall(function()prev_proto:call(tvb, pinfo, tree)end)

            if not f_udp() then return end

            local ofs = udp_dumper_proto.prefs.ofs -- udp_dumper_proto.prefs.filter
            if (tvb:len() < ofs) then return end

            -- this is just to add text to "udp_dump.data" field, 
            -- which you should display as column.
            -- as an alternate, you may remove set_hidden() and view selected data in the treeview
            tree:add(udp_dumper_proto.fields.dump, tvb(ofs,1)):set_hidden();
        end

        -- if we hook upon UDP port, then offset will mean the beginning of the UDP data
        udp_table = DissectorTable.get("udp.port")
        prev_proto = udp_table:get_dissector(udp_dumper_proto.prefs.port)
        udp_table:add(udp_dumper_proto.prefs.port, udp_dumper_proto)

        -- if we hook as post dissector, the offset will be from start of the frame. 
        -- don't forget to remove the prev_proto call if you'll use that kind of hook
--        register_postdissector(udp_dumper_proto)
end