Distances are measured in Leagues, each League is about an hour of travel on a road (or 3 miles). Majority of characters will travel at this rate unless they have a reason to move significantly faster or slower.
In general a character will travel 7 hours a day, with 1 hour of resting at mid-day. Characters must consume 2 rations per day of travel. Rations can always be bought at towns and waystations for relatively cheap (less than a coin).
Pack animals do not allow for faster travel, unless they are special in some way. They do allow for more gear to be carried, such as supplies or loot.
Rough Terrain, such as traveling cross country will half the travel rate. Characters will likely also have to roll a check to avoid getting lost and surpass barriers such as creeks and cliffs. Taking pack animals cross country can be a terrible idea for this reason.
When traveling long distances where Encounters could occur. Decide a duration for a Round, a round could be 1 day, 1 rest (twice a day/every 4 hours), every hour (for example on a hex-map) or even faster in densely populated terrain.
Roll dice for each round, dice starts at d20, when rolled the dice decreases one size (d20 > d12 > d10 > d8 > d6 > d4). On 1 encounter is triggered and dice resets.
On a 2-3 a distant encounter is rolled, but is spotted on the horizon, which can easily be avoided or approached at the players choice. This only resets the dice if the encounter is approached.
Encounter's should be unique to the area and/or situation. In a safe location encounters should be relatively benign, such as patrolling guards or roaming hunters. Dangerous encounters could be poachers or wild animals.