Is it better to book everything in advance?

No. Book your first two nights in each new country, but leave the rest flexible. Flexibility is the biggest perk of backpacking.

Do I need a massive backpack?

Keep it under 40 liters. If you can't carry it for 20 minutes comfortably, it is too heavy. You will regret a big bag on crowded buses.

Planning a Backpacking Route Through Southeast Asia

Focus your route on a logical loop starting and ending in Bangkok, which acts as the region's main air hub. Limit your pace to one major destination every 4-5 days to avoid burnout and keep total transport costs manageable.

Establish your anchor points. Pick three countries max for a 30-day trip. Popular first-timer routes connect Thailand, Laos, and Vietnam. If you have 60 days, include Cambodia and a slice of Indonesia or the Philippines.
Map your transport spine. Use the 'Banana Pancake Trail' as a skeleton but deviate. Book long-distance transport—like overnight trains in Thailand or domestic flights in Vietnam (VietJet/AirAsia)—at least 1 week in advance during peak season.
Balance city and nature. Alternate high-energy urban environments like Bangkok or Hanoi with slower-paced locations like Luang Prabang or islands in the Thai Gulf to manage your energy levels.
Calculate buffer days. Always add one 'nothing' day for every week of travel. You will get sick, miss a bus, or simply need a day to do laundry and sit in a coffee shop.

Is it better to book everything in advance?: No. Book your first two nights in each new country, but leave the rest flexible. Flexibility is the biggest perk of backpacking.
Do I need a massive backpack?: Keep it under 40 liters. If you can't carry it for 20 minutes comfortably, it is too heavy. You will regret a big bag on crowded buses.