I've just whipped up a Python script that renders Github issue lists from your favourite projects as an iCalendar feed.
It is really easy to get up and running. All the dependencies are available on a modern Linux distribution, for example:
$ sudo apt-get install python-yaml python-icalendar python-flask python-pygithub
Just create an API token in Github and put it into a configuration file like this:
api_token: 6b36b3d7579d06c9f8e88bc6fb33864e4765e5fac4a3c2fd1bc33aad bind_address: ::0 bind_port: 5000 filter: all
Run it from the shell:
$ ./github_icalendar/main.py github-ics.cfg
and connect to it with your favourite iCalendar client.
A single iCalendar client can usually support multiple sources and thereby consolidate lists of issues from multiple bug trackers.
This can be much more powerful than combining RSS bug feeds because iCalendar has built-in support for concepts such as priority and deadline. The client can use these to help you identify the most critical issues across all your projects, no matter which bug tracker they use.
Bugzilla bugtrackers already expose iCalendar feeds directly, just look for the iCalendar link at the bottom of any search results page. Here is an example URL from the Mozilla instance of Bugzilla.
The Ultimate Debian Database consolidates information from the Debian and Ubuntu universe and can already export it as an RSS feed, there is discussion about extrapolating that to an iCalendar feed too.