Josh, I have a little bit of experience of that part of the world ... and whilst I applaud your "can do" attitude ... and you are a Brit and so am I ... some of what you are planning is unlikely to be doable.
The beginning of your journey is OK ... you don't need a visa to get into Tunisia for less than a three month stay with a British Passport ... so flying into Tunis is possible but bear in mind that a few Contractors who wanted to work in Libiya were going into Tunis and then trying to get across the border with Libiya not that long ago ... so flying in with a knife in a rucksack with a load of camping gear may lead to the possibility of confiscation of the knife at the airport and a load of other gear or you enter the grey zone of how much it might take to pay to keep it ... where diplomatic questions like "can't I pay a fine" and keep it as I need it ?" might sort you out ... but keep the knife sterile so there are no Busse labels on it ... otherwise a quick bit of "google-fu" and the "fine" you might have been offered will be a lot more or it will be kept altogether ...
So consider travelling with a disposable suit case ... so all the gear is in it and seperately packed ( i.e. don't just put a packed rucksack into the suit case as even there they have X rays ) ... and try and seem as "package holiday" as possible ...
However having said that ... whilst the border is open with Algeria from Tunisia ... you won't get into Algeria without a visa which you need to acquire in the UK prior to setting off ... and it is doubtful that the Algerians will grant a visa for this when you tell them where you are going ...
Here are some issues ... check out the site below ...
http://www.fco.gov.uk/en/travel-and...e-by-country/middle-east-north-africa/algeria
Kidnap is a serious problem ... particularly the closer you get to Mali ... see the plight of the spanish and italian workers in the refugee camps ...
Then there is the crossing into Mali to get to Timbuktu ... Mali is so dangerous that the British Foreign Office has withdrawn it's embassy in Mali ... visa permits cannot be obtained ... you can seek help from other EU countries such as the French ... but I would'nt think they will be more help either ...
So I am thinking you might be trying to cross the border from Tunisia without a visa ... don't ! Prisons in Algeria are HIV death traps ... male rape is common ...
Kidnap and ransom insurance is unlikely to be offered to you ... even if you had the Visa ... but you can PM me for details on this if you want to try ...
In your situation I would consider altering my route ... and trying for some sort of charitable "walk" status ... or some form of backing which had an organisation to try and look after you ... not that this will radically help ... the refugee camp workers had this and they are still missing ... and in 2009 the kidnap victim was killed ...
All told ... I think it is a bit too high on the risk front ... and I am not risk averse ...
Why not consider walking across Algeria by a coastal route ? The nearer you are to the northern coast line the safer it is ... if you try this then the advice needed mellows to common sense things like don't go into Algeirs at night ... approach all cities where you have to walk through the suburbs by day ... ideally early morning ... both in and out ...
Consider being able to afford a satellite phone too ... a coastal walk is likely to be insurable for K&R ... if you have a policy and keep track of where you are if anything kicks off ... you are able to make an emergency call and have some back up which would be effective ...
Down in the south of Algeria ... it is much harder to get any help ... whereas near the coast ... some nice gentlemen can drop in and help out if need be ... and probably for that very reason ... it is less likely to happen ... :thumbup: